Nutritional Recommendations for People with Type 1 Diabetes Mellitus

Introduction

This clinical practice guideline is aimed at all people with type 1 diabetes (T1Dm) and all professional groups that care for people with T1Dm.

In accordance with the demand for individualisation of therapy, counselling, empowerment and diabetes self-management [1] [2] and in view of the Consensus Report “Nutrition Therapy for Adults with Diabetes or Prediabetes” [3] [4] the DDGʼs Nutrition Committee has set itself the goal of developing evidence-based practical recommendations on nutrition that are specific to target groups for to present the different (sub-)types of diabetes mellitus. In the clinical practice guidelines on diet in T1Dm presented here, it is clear that the evidence for general recommendations is limited. Individual testing (CGM) of the glycaemic effects of food intake is important in many aspects of nutrition. These determined empirical values – in addition to the patientʼs own food preferences – provide a suitable basis for individual food selection and the appropriate strategy for insulin application.

Nutritional aspects in relation to glycaemia and glycaemic target parameters

Estimation of carbohydrate quantities

Recommendation

Patients should

• Be able to correctly estimate the amount of carbohydrates (CHO) ingested per meal to an accuracy of 1 carbohydrate unit (CU), equivalent to 10 g of CHO (as a basis for algorithm-guided dosing of prandial insulin),

• Know their individual postprandial glucose trends,

• Repeat testing of a standardised meal, ideally via CGM.

Comment

Although there are few evidence-based studies available, it is of crucial importance for the treatment of T1Dm that patients are able to assess the glucose efficacy of their diet in order to adjust insulin dosage accordingly [5] [6] [7]. Repeated structured training courses should create the basis for this [5] [7].

There is no recommendation on the amount of carbohydrates and must be considered individually [6] [7]. CGM data can help when choosing the optimal bolus variant or the correct injection-to-meal interval [8]. In the case of gastroparesis, the control of different bolus variants can ensure an individually adapted trend. Patients on fixed doses and pregnant women in particular need to estimate the correct amount of CHO in their meal [6].

Especially for children and adolescents, an individualised diet and the corresponding monitoring and adjustment of the insulin dose algorithms can lead to better acceptance of the disease. Currently, estimating the consumed carbohydrate (CHO) amounts is also recommended when using AID (Automatic Insulin Dosing) systems – with preprandial input of the CHO amount into the system. Metabolizing the carbohydrate uptake solely via the AID autocorrection cannot be recommended at present despite extensive experience. The currently-available systems are also not approved for this. In the event of an AID system failure, the correct estimation of CHO quantities must be taught and mastered.

Glycaemic Index (GI)

Recommendation

• The individual testing of the glycaemia response (by glucose self-monitoring) to the preferred foods and meals is of great importance in order to develop and implement an adequate individual prandial insulin application strategy (e. g. via injection timing and mode of application in continuous subcutaneous insulin infusion [CSII]).

• There is no evidence that generally giving preference to low GI carbohydrate carriers helps people with T1Dm achieve their therapy targets.

• For individual meals, it is recommended to cover carbohydrate-rich foods with a low GI (below approx. 30) with significantly less prandial insulin in order to prevent hypoglycaemia, especially in the case of an almost normoglycaemic metabolic control.

Comment

There are many GI tables in circulation, but only a few are published in scientific papers [13] [14] [15]. In order to assess the GI, it should be taken into account that the GI values are basically average values from several studies. Variety, degree of ripeness, place of cultivation/production and, if applicable, recipe of a food item all have a decisive influence on the GI. For bananas, for example, an average GI of 48 (ref. glucose=100%; volunteers: T2Dm) is reported – with a range of GI 30 to GI 58 for the 9 studies considered [13]. For cooked white rice (mean GI: 59), the range even goes from GI 43 to GI 112 [13].

Studies of adults with T1Dm under experimental conditions that compared the blood glucose response to (single) whole meals with low vs. high GI [16] [17] [18] have found significantly lower blood glucose responses after low GI meals and observed hypoglycaemia when low GI carbohydrate carriers (lentils) are covered with the usual dose of mealtime insulin [16].

Medium- and long-term studies on the effects of an average low-GI diet vs. an average high-GI diet in adults with T1Dm under everyday conditions are scarce; they date back mainly to the 1990s and had few participants [17] [19].

In a meta-analysis from 2010 [20], 2 studies in adults with T1Dm were included; however, they exhibit methodological deficiencies and are not relevant for statements on GI [21] [22]. A more recent review on the relevance of GI in adults from 2018 did not include people with T1Dm [23].

No favourable recommendations could be derived for children and adolescents with T1Dm [24] [25] [26]. A study from 2001 [27] which is often used as an argument for the advantage of a low-GI diet, was not justified, as the study did not intend to compare a low-GI diet with a high-GI diet, but primarily compared a diet with a fixed carbohydrate distribution (“CU framework”) vs. a diet with flexible CHO intake and found identical values for the mean GI of the carbohydrate carriers consumed.

Foods with a very low GI (below approx. 30: e. g. pulses, nuts) should be covered with less prandial insulin to avoid hypoglycaemia in the case of almost normoglycaemic preprandial blood glucose values, while foods with a very high GI (especially sugar-sweetened drinks) are more likely to be reserved for self-treatment of hypoglycaemia.

Individual testing of the glycaemic response (through glucose self-monitoring) to the preferred foods and meals is of great importance, similar to finding an optimal personal strategy for physical activity in diabetes.

The evaluation of postprandial glucose trends via CGM can help to select the appropriate insulin dose and bolus variant or injection-to-meal interval. People with ICT therapy can act with the options of injection-to-meal intervals or split boluses. People with CSII therapy can act via dual boluses/multiwave boluses or delayed boluses and injection-to-meal intervals. Basic criteria for the decision are initial glucose levels, carbohydrate amounts (CU) and the GI of the food. (Night-time) hypoglycaemic events resulting from evening meals with a very low GI must be prevented.

In practice, it has proven to be useful to vary the time of injection or, in the case of CSII, the insulin application mode for certain foods and starting situations according to personal experience.

Insulin requirements for protein and fat-rich meals

Recommendation

• There is no evidence that people with T1Dm generally estimate their meals quantitatively for energy, fat and protein content in order to derive an additional insulin bolus.

• The blood glucose response to very high-fat or high-protein meals varies from person to person and should be determined and documented by self-monitoring. On this basis, an additional insulin requirement may be developed individually.

• Increasing the prandial insulin dose for high-protein evening meals increases the risk of night-time hypoglycaemia.

• People with T1Dm should be able to assess the effect of fats and proteins on glucose levels.

Comment

Protein-rich meals also result in a certain insulin requirement and can lead to postprandial delayed and sustained hyperglycaemia [28] [29] [30]. With a carbohydrate intake of about 50 energy percent (EN%) and the remaining distribution to fat and protein, about 50% of the total insulin is distributed to the fast-acting mealtime insulin and 50% is covered by the basal supply. People with T1Dm who have a low carb diet have a correspondingly higher basal rate and a lower proportion of mealtime insulin. However, there are situations in which low carbohydrates, high fat and protein are eaten with the main meal or in which a high proportion of fat and protein is ingested in the evening in the form of nuts, for example. In these cases, a simple bolus via mealtime insulin is usually not sufficient. One way to cover the slow glucose increase as a result of such meals would be, for example, a correction with fast-acting mealtime insulin at a later time. With CSII therapy, it would also be possible to give a delayed bolus. In order to know how much bolus to give, the FPU (fat-protein unit) was propagated as a measure.

According to Pankowska, 100 kcal of fat and protein are calculated as one CU and, depending on the amount of FPU, are delivered as a delayed bolus for a maximum of 8 h [28] [31]. In practice and in various studies, however, it has been observed that this formula cannot be used equally well for all people with T1Dm. In a paper by Hermann, a calculation with 200 kcal corresponding to one CU was compared [32]. This paper confirmed that hardly any formula can be applied equally well to everyone. The same result was also obtained in a pilot study with nuts [33]. Glucose increases can be observed after eating foods rich in fat and protein, but the insulin dose must be determined and learned individually. Increasing the prandial insulin dose for high-protein evening meals increases the risk of night-time hypoglycaemia.

Fibre and glycaemic control

Recommendation

• There is not yet sufficient evidence that people with T1Dm should eat a high-fibre diet to achieve their glycaemic therapy target.

• Possible effects of a fibre-rich diet on other health-promoting aspects (e. g. cardiovascular diseases, intestinal health, weight management) should be considered separately and individually.

• The increased consumption of high-fibre foods seems to have a positive effect on the trend of postprandial glycaemia, but the recommendations for fibre intake are based on those for the general population (30 g per day).

Comment

The German Nutrition Society (Deutsche Gesellschaft für Ernährung) recommends a daily intake of at least 30 g of dietary fibre for the general population, which is not achieved by the average German population [34]. So far, there are no evidence-based recommendations for a certain amount of dietary fibre in diabetes.

In terms of weight management, dietary fibre plays a strong role, at least in T2Dm, when consumed as part of a diet that has a low glycaemic index [35]. Dietary fibre contributes to a reduction in energy density and a decrease in the glycaemic index and positively modulates the blood glucose profile. Observational studies in subjects with T1Dm have also shown an association with lower HbA_1c levels [36].

Consumption of sucrose and fructose

Recommendation

• Beyond the general recommendations, there is no evidence of specific recommendation for reducing added sucrose in individuals with T1Dm.

• Foods containing naturally-occurring sugars (glucose and fructose) should not be restricted in the diet of people with T1Dm.

• The evidence base for the recommendation of a reduction of added fructose is uncertain.

Comment

Due to the limited evidence regarding recommendations for sucrose and fructose consumption in T1Dm, current evidence-based guidelines generally recommend that people with diabetes mellitus minimise the intake of these and replace them with foods with a higher nutrient density [3] [5] [6]. Recommendations that state a suggested upper limit usually set this at 10 EN% for adults and 5 EN% for children > 2 years [47]. However, according to the American Dietetic Associationʼs dietary recommendations for individuals with T1Dm and T2Dm, a sucrose intake of 10–35 EN% has no negative effects on the glycaemic or lipid response when sucrose is replaced isocalorically for starch [38].

Use of sweeteners

Recommendation

• Sweeteners can be useful as an occasional addition to foods and beverages as part of a diabetes-compliant diet and insulin therapy and are harmless to health as long as they are consumed below the respective maximum amounts.

Comment

In general, research on sweeteners is hampered by the chemical and metabolic heterogeneity of sweeteners, their at times combined use in different product groups and the changing trends in consumer behaviour [39] [40]. Even though the calorie content of some sweeteners is 4 kcal/g, just like conventional sugar (sucrose), they are only used in very small amounts in the milligram range due to their high sweetening power, so that calorie intake is negligible. The European Food Safety Authority (EFSA) specifies acceptable daily intake levels (ADIs) in each case, which correspond to the amount of an additive that can be ingested per kilogram of body weight per day throughout life without any health risks. Although sweeteners are therefore considered to be harmless to health according to the current state of knowledge, possible long-term health consequences in particular have been repeatedly discussed for many years.

The reservation of an increased cancer risk from sweeteners is mainly based on older studies, which are based on results from animal experiments. However, these studies used very high amounts of the sweetener in question, far in excess of the acceptable daily intake for humans, so that the results are not transferable to humans. According to recent animal studies and available human data, there is no evidence of an increased cancer risk from sweeteners if the ADI values are adhered to [39] [41].

An increase in weight caused by sweeteners has not yet been scientifically proven. The clinical studies on this topic sometimes diverge considerably [42] [43].

Some observational studies show a positive association between sweetener consumption and the risk of T2Dm and other cardiometabolic diseases, but the bias of excess weight and reverse causality is often a problem [39] [42] [44]. Regarding the effect of sweeteners on appetite, intervention studies show that beverages containing sweeteners have an effect similar to water on appetite and energy intake [43] [45] [46] [47].

The potential benefit of sweeteners in patients with T1Dm is mainly due to their use as a substitute for sugar without triggering a glycaemic response. Despite controversial discussions, current research provides collective evidence that the consumption of sweeteners has no adverse effects on blood glucose and insulin regulation (HbA_1c, fasting and postprandial glucose and insulin levels) in people with and without diabetes [43] [48].

Effective blood glucose foods for hypoglycaemia

Recommendation

• Persons with T1Dm and mild hypoglycaemia (can be treated by the patient) should consume 15–20 g of rapidly absorbable carbohydrates. This measure should be repeated after 15 min if blood glucose concentrations remain low.

• Persons with T1Dm and severe hypoglycaemia experiencing confusion or clouding of consciousness should consume 30 g of rapidly absorbable carbohydrates. In individual cases, it may be necessary to supplement with 15–20 g of slowly resorbable carbohydrates.

Comment

Rapid carbohydrates such as oral glucose in solid and liquid form are particularly suitable for treating hypoglycaemia. Furthermore, sucrose-containing beverages such as lemonades and juices can be used.

In some cases and depending on the situation, slowly resorbable carbohydrates can contribute to the stabilisation of blood glucose [5] [6] [7].

In order to preventatively avoid hypoglycaemia, in special situations, rapidly resorbable carbohydrates should be ingested beforehand to increase the target value and slowly resorbable carbohydrates should be supplemented to stabilise the trend. The amount should be chosen individually and depend on the situation. Physical activity and alcohol consumption are classic situations where consequences can result in hypoglycaemia [5].

People who suffer from severe hypoglycaemia, who can no longer perform self-therapy or who are unconscious should not be given oral carbohydrates. In these cases, it is either possible for family members or relatives to administer glucagon or for professional IV glucose administration. Friends and family members should be trained in the use of glucagon kits [49].

General nutrition aspects

Protein consumption

Recommendation

• There are contradictory statements regarding the benefit/damage for limiting or increasing protein intake as part of a specific diabetes diet. At most, a limitation of the daily protein intake may be useful under a few specific circumstances in existing kidney diseases.

Comment

Increased protein consumption has been scientifically studied in people with type 1 diabetes mellitus, particularly with regard to the acute glycaemic response [50]. In this context, we refer to the recommendation in the section on “Insulin requirements for protein and fat-rich meals”.

No evidence has been shown that increased protein intake leads to positive or negative effects in people with T1Dm.

A limitation of protein intake has been studied, especially with regard to slowing the progression of diabetic nephropathy.

In general, randomised controlled trials (RCTs) with intervention times > 6 months show that protein targets < 0.8 g/kg body weight/d are rarely met – even under study conditions.

In a larger randomised controlled trial, a low-protein diet in people with T1Dm or T2Dm and nephropathy achieved significant improvements in glomerular filtration rate when compliance was good [51].

In another methodologically well-conducted study, limited protein intake also appeared to slow the progression of diabetic nephropathy, but the effects were not significant. Compliance was also poor in this study and difficult for patients to maintain. Another study showed no difference in the rate of progression of diabetic nephropathy with low normal protein intake (0.8 g/kg body weight, 16 EN%) vs. high normal protein intake (19 EN%) [52].

General nutrition aspects

Fat intake

Recommendation

• No specific recommendation can be made for the amount of fat intake in people with T1Dm.

• Effects of the fatty acid composition (fat quality) on other health-promoting aspects may need to be considered separately. However, the fat quality should be in accordance with the recommendations for the general population.

Comment

For the acute blood glucose response after fat intake, please refer to the section “Insulin requirements for protein and fat-rich meals”.

The popularity of low-carbohydrate and thus mostly high-fat diets is high. However, high-fat and low-carbohydrate diets have not been well studied in the treatment of T1Dm. Studies that looked at glycaemic outcomes from low-carbohydrate diets were mostly cross-sectional studies without validated nutritional data and without control groups. Participants were highly motivated, self-selected individuals who used intensive insulin management practices, including frequent blood glucose monitoring and additional insulin corrections with narrow glycaemic targets. For this reason, these results are not necessarily transferable to patients with type 1 diabetes in general. Carbohydrate-containing foods such as cereals, fruits and milk are important sources of nutrients, and such diets require attention to vitamin and energy intake to avoid micronutrient deficiencies and growth problems in children. Following restrictive diets is a challenge and can affect social normalcy. People with T1Dm also theoretically have adverse health risks such as diabetic ketoacidosis, hypoglycaemia, dyslipidaemia and glycogen deficiency [53].

In general, high fat intake and low carbohydrate intake are often associated with a higher BMI in observational studies [54], but this does not lead to the conclusion that low fat and high carbohydrate intake is generally recommended. The quality of the fats and carbohydrates consumed is often not addressed in observational studies, so that it is not taken into account that too much low-quality fat and too little complex carbohydrates are usually consumed (see also DDG statement on recommendations of the American Diabetes Association (ADA) 2019 [4]).

Instead, randomised, controlled intervention studies evaluating the quality of macronutrients should be considered to answer the question of changing the fat intake for people with T1Dm.

Eating patterns

Recommendation

• There are a variety of dietary patterns that are suitable for people with T1Dm. The available evidence is insufficient to recommend one specific dietary pattern for successful diabetes management.

Comment

A diet based on the Mediterranean diet or the Dietary Approaches to Stop Hypertension (DASH) diet could help improve glucose metabolism and weight control and reduce cardiovascular risk factors. However, low-carbohydrate, vegan/vegetarian, plant-based diets, or a diet rich in legumes can also be suitable for people with diabetes. Individual preferences, goals and needs should influence the choice of dietary pattern [5] [6] [7]. Even specifically for people with T1Dm, the American Diabetes Association says that there is insufficient evidence to make one dietary pattern more recommended than another [5].

In 96 children and adolescents with T1Dm, structured nutritional training for a Mediterranean diet improved the quality of nutrient intake, followed by an improvement in serum lipid levels [55]. In a 5-year longitudinal observational study of 500 children and adolescents with T1Dm, greater adherence to the Mediterranean diet was also associated with better glycaemic control and better serum lipid levels [56].

However, in a preliminary controlled intervention study in 16 adolescents with T1Dm, participants on the DASH diet were shown to have increased glycaemic variability compared to their usual diet. Adapting the DASH diet to people with diabetes (e. g., 30 EN% from fat instead of 20 EN%) resulted in a glycaemic variability comparable to the usual diet, but with lower average blood glucose concentrations and less time in the hyperglycaemic range [57].

Greater adherence to whole grains, fruits, vegetables, legumes, nuts, and seeds was associated with better glycaemic control in a longitudinal observational study in adolescents with T1Dm [50].

In addition to the evidence for the above described hypothesis-based dietary patterns, 4 cross-sectional and one longitudinal observational study investigated associations between exploratory dietary patterns and metabolic parameters such as glycaemic control and blood pressure, inflammatory biomarkers, serum lipid levels, and vascular health parameters in subjects with T1Dm [58] [59] [60] [61] [62]. These studies also confirm the conclusion of medical societies that there are a variety of dietary patterns that may be beneficial for people with diabetes, in this case T1Dm [5] [6] [7].

More than a third of all people with T1Dm follow a special diet. Predisposing factors for this are being a female, a longer duration of diabetes and various diabetes complications. About 7% of patients with T1Dm follow a vegetarian diet [63]. By means of adapted insulin therapy, good metabolic control is possible in people with T1Dm who follow a vegetarian diet [64]. Among the various forms of a vegetarian diet, the ovo-lacto-vegetarian diet is the most common. In the study by Ahola AJ et al., the carbohydrate content of a vegetarian diet was only slightly higher than that of people without special diets and, at 45 EN%, corresponded to the general recommendations [63]. Nevertheless, when switching to a vegetarian diet, the need to monitor and adjust the insulin dose should always be checked [65]. Low GI carbohydrates should also be given preference, preferably together with fibre, protein or fat, to prevent a rapid rise in blood glucose [66]. In fact, patients with T1Dm have a high fibre content and folic acid levels in their diet [63]. A vegetarian diet often results in a risk of an insufficient vitamin B12, and appropriate checks are therefore indicated in order to initiate any necessary supplementation [67]. With regard to HbA_1c levels, a significant improvement of about 0.4% can be achieved after switching to a vegetarian diet [68]. In addition to this, a plant-based diet has a specific effect on kidney function in people with T1Dm compared to a meat-based diet [69] and a change in diet to a vegetarian diet can have a favourable effect on the progression of diabetic nephropathy [70]. However, it should be noted that young women in particular who are intensively involved with their diet, for example in the context of vegetarianism, exhibit an increased risk of eating disorders [71]. Plant-based alternatives to meat can also lead to undesirable side effects, such as hypogonadism and erectile dysfunction as a result of eating soy products [72].

Meal frequency and meal timing

Recommendation

• If people with T1Dm are overweight, they should avoid irregular eating times, eating late and a time window for daily food intake > 12 h. Instead, they should consume the calories predominantly in the first half of the day, as this can have a beneficial effect on body weight regulation and cardiometabolic risk.

• A recommendation for fasting during the day (meal skipping, < 3 meals per day) or modified intermittent fasting on one or more days a week cannot be given.

Comment

Irregular food intake, such as skipping meals and snacking behaviour, where small portions are often eaten between meals and almost around the clock, is a characteristic of the modern lifestyle [73].

A high meal frequency can increase the risk of obesity [74] [75], as many small meals lead to less satiety than 3 larger meals with the same energy intake [76] [77]. In addition, frequent smalls meals compared to fewer meals with the same energy intake resulted in higher liver fat content [77] [78].

On the other hand, lower meal frequency, lower caloric intake at breakfast or complete skipping of breakfast was associated with higher weight gain and increased risk of diabetes, heart attack and stroke in prospective long-term studies [79]. Intervention studies of varying durations provide further evidence that skipping breakfast and/or lunch does not have consistently positive effects on body weight regulation or glucose metabolism [74] [80] [81], [82] [83]. By contrast, skipping the evening meal and eating three meals until early afternoon resulted in an improvement in insulin sensitivity, β-cell response, blood pressure, and appetite compared to an isocaloric breakfast-lunch-dinner protocol [84] [85].

The influence of the time of mealtime intake on body weight and cardiovascular and metabolic risk is partly explained by circadian differences in metabolism (e. g. with regard to insulin sensitivity). On the other hand, the circadian clock, with the help of clock genes and clock-controlled genes, uses food intake as a timer, so the timing of meals can have an influence on the energy balance and metabolic risk [86]. If food is consumed mainly in the evening or at night, contrary to the natural circadian rhythms, e. g. by skipping breakfast, this leads to lower postprandial thermogenesis and higher postprandial glycaemia and insulin response [87]. Consuming foods with low glycaemic GI in the morning leads to a greater improvement in glycaemia than if these foods were consumed in the evening [88].

In addition, a long daily time window during which food is consumed and energy thus ingested, promotes weight gain independent of the time of food intake [73]. A reduction of the daily time window during which food was eaten from more than 14 h to 10–12 h led to weight loss with an otherwise unchanged diet [89].

Intermittent fasting is a popular concept for weight loss based on major cycles of dietary restriction, which do not involve skipping a single meal, but instead provide a greatly reduced calorie intake (0 to < 25% of energy requirements) every 2nd day or 2–3 times a week. Intermittent fasting results in significant weight loss depending on the frequency of the fasting days, but this is no different from the success of a reduction diet with continuous energy restriction [90] [91] [92] [93]. The effects of this negative energy balance lead to a varyingly pronounced reduction of cardiometabolic risk factors dependent on the initial values.

There are worries that intermittent fasting increases the variability of glycaemia by increasing the risk of both hypoglycaemia and postprandial hyperglycaemia [94] [95]. The lack of superiority of intermittent fasting over continuous, moderate calorie restriction and the lack of studies on the risks and long-term results in people with T1Dm make it impossible to recommend intermittent fasting.

Recommendations for body weight

Recommendation

• People with T1Dm and normal weight should maintain a normal body weight.

• The study situation is not sufficient to generalise the recommendation to lose weight to overweight people with type 1 diabetes. However, the recommendation for losing weight may be useful in the presence of concomitant diseases or insulin resistance (e. g. secondary dyslipoproteinaemia, high blood pressure, steatohepatitis, etc.).

• It is important to consider the quality of food and possible hypoglycaemia (especially in low-carb diets) as well as the development of eating disorders.

Comment

A higher body mass index (BMI) is associated with macrovascular disease and retinopathy in T1Dm [5] [6]. There are no evidence-based studies showing an association between weight and glycaemic control in T1Dm. However, it can be assumed that weight loss in T1Dm with simultaneous insulin resistance or parallel metabolic syndrome would be the same as for T2Dm [57] [89] [96].

Therefore, a diet with a low caloric density but high nutritional quality is beneficial for weight reduction in obese T1Dm patients, especially if the aim is to predominantly reduce abdominal fat.

Very-low-carb diets, formula diets or interval fasting may increase the risk of hypoglycaemia and should be used only with close monitoring and adjustment of the insulin regimen and discussed with the diabetes team.

There is no scientific evidence for the superiority of one nutritional concept (e. g. low-carb or low-fat) in terms of weight loss for T1Dm. Very-low-carb diets or interval fasting can increase the risk of hypoglycaemia and should therefore only be used with close monitoring of the insulin regimen.

Particularly with the somewhat younger T1Dm patients, the patientʼs desire to lose weight must be critically viewed against the risk of developing an eating disorder. Female patients are more vulnerable than male T1Dm patients, [97].

Dietary recommendations for weight maintenance

Recommendation

• There is no specific recommendation for maintaining weight with T1Dm.

Comment

Studies on the optimal diet for weight maintenance at T1Dm are not available. The recommendations should be based on the German Nutrition Society (Deutsche Gesellschaft für Ernährung - DGE) guidelines for healthy individuals, but without defining a specific proportion of macronutrients.

Nutritional intervention studies without weight loss differ in the metabolic outcome. With the Mediterranean diet (n=96) the lipid profile improved; with the low-fat diet (n=10) insulin sensitivity in T1Dm patients was also reduced [98].

In individual cases and when used in moderation, carbohydrate reduction can be safe and with few side effects but also without particular benefit (Case Report) [99]. The risk of hypoglycaemia increases, however, when rapid-acting insulins are used with “low carb” diets [100]. By contrast, other studies show a reduction in the hypoglycaemia risk just by significantly reducing carbohydrate intake (< 50 g; n=10, 1 week). Ketonuria as an indicator of insulin deficiency is limited [101]. The effectiveness of emergency glucagon is also reduced due to the lower liver glycogen content [102].

Diets rich in carbohydrates are without advantage or disadvantage when the insulin dose is adjusted (n=9; 4 weeks) [103]. High-fibre versions of such diets have lower insulin requirements (n=10; 4 weeks) [104], but can be associated on the other hand with a worsening of the metabolic state – even during intense physical activity (n=7, 3 weeks) [105].

Nutritional aspects in geriatric patients

Recommendation

• There are no special dietary recommendations for elderly or geriatric persons with T1Dm.

• The goals in nutritional counselling often have a different focus and address maintaining independence more than the actual glycaemia and, in geriatric patients, on avoiding malnutrition and hypoglycaemia.

• The recommendations of a protein intake that meets the needs (at least 1 g/kg body weight/d) and the maintenance of a BMI that is normal to slightly overweight are two basic recommendations that apply to both the general population and this group of people.

Comment

Basically, the nutritional recommendations for older people with T1Dm do not differ from those for older metabolically healthy or younger people with T1Dm. However, in functionally-dependent patients, the consequences of malnutrition in advanced age are serious and the recommendations for geriatric patients with T1Dm should be followed.

The S2k clinic practice guideline “Diagnosis, Therapy and Follow-up of Diabetes in the Elderly” (Diagnostik, Therapie und Verlaufskontrolle des Diabetes im Alter) also contains very detailed recommendations on nutritional counselling for older persons with diabetes.

Although an improvement in insulin sensitivity can also be achieved in the elderly through intentional weight reduction [106], strict dietary guidelines should be avoided in the elderly with excess weight or obesity because of the risk of malnutrition. If weight loss is considered, dietary measures should be combined with physical activity whenever possible and should focus on meeting protein intake requirements. A significant increase in mortality was found in those over 65 years of age only above a body mass index (BMI) of 30 kg/m² [106]. Patients perceive limiting the consumption of familiar and comfort food as a reduction in what they consider quality of life. This aspect is of decisive importance, especially for people of advanced age.

The risk of potential malnutrition is present when there is a persistent reduced food intake (approximately < 50% of requirements for more than 3 days) or when several risk factors are present simultaneously that either reduce the amount of food eaten or significantly increase energy and nutrient requirements. The risk of malnutrition can be assessed e. g. by MNA or the corresponding short form (SF-MNA); both screening methods are well evaluated [107], [108].

Nutritional counselling should also focus on the prevention of hypoglycaemia, with an initial focus on the adjustment of medication.

Nutritional aspects of special foods and food supplements

Sugar-sweetened beverages

Recommendation

• With the exception of treating hypoglycaemia, people with T1Dm should minimise their consumption of sugar-sweetened beverages.

Comment

Similar to the evidence for sucrose and fructose intake in people with T1Dm, the data on the consumption of sugar-sweetened beverages specifically for this group of patients is also limited, so that recommendations made for the general population and for people with diabetes in general must also be used. According to the current evidence-based guideline of the American Diabetes Association, the consumption of sugar-sweetened beverages is strongly discouraged for people with diabetes. Instead, drinking water is recommended as often as possible to control blood glucose levels and body weight, and reduce the risk of cardiovascular disease and fatty liver (evidence level B) [3] [5]. The British Diabetes Society agrees that reducing the consumption of sugar-sweetened drinks reduces cardiovascular risk but only rates the evidence on reducing the consumption of sugar-sweetened drinks as low (Grade 2) [6].

Alcohol

Recommendation

• People with T1Dm should limit the amount of alcohol consumed to the amounts recommended for the general population. Moderate, low-risk alcohol consumption is compatible with good metabolic control and diabetes prognosis.

• People with diabetes and risky alcohol consumption or an alcohol dependency should be informed about the dangers of alcohol, especially with regard to poorer metabolic control and the risk of secondary complications.

• It should generally be noted that consumption of larger amounts of alcohol increases the risk of severe hypoglycaemia, especially at night. This risk can be reduced by eating during the period of alcohol consumption and raising the target blood glucose level for the night.

Comment

People with diabetes should be advised of the effects of alcohol consumption on blood glucose levels and, if alcohol is consumed, should be encouraged to stick to low-risk consumption amounts. The German Head Office for Addiction Issues e. V. (Deutsche Hauptstelle für Suchtfragen e. V. – DHS) defines 12 g alcohol per day for women and 24 g alcohol per day for men as limits for low-risk consumption. The World Health Organization (WHO) defines a consumption of 10 g alcohol per day for women and 20 g alcohol per day for men as low risk. These amounts also apply to people with T1Dm.

The consumption of alcohol can affect blood glucose counterregulation and thus increase the risk of hypoglycaemia. About one in five cases of severe hypoglycaemia resulting in hospitalisation is caused by alcohol consumption. The main effect of alcohol results in reduced awareness, which leads to a limited hypoglycaemia perception and thus prevents patients from reacting appropriately. A systematic review on this issue is available from 2018 [109] where a total of 13 studies (RCT and observational studies) were evaluated.

Eight studies reported that ethanol – regardless of whether administered intravenously or orally – was associated with an increased risk of hypoglycaemia, which was linked with a decrease in plasma glucose, an impaired counterregulatory response, hypoglycaemia perception disorder, and impaired cognitive function.

Five studies did not prove an increased risk of hypoglycaemia. None of the studies examined prevention strategies for ethanol-induced hypoglycaemia. Recommendations from 13 diabetes associations were included. All associations recommend only consuming ethanol together with the consumption of food. The majority of the included studies showed that ethanol consumption increased the risk of hypoglycaemia in patients with T1Dm. However, the evidence for the prevention of ethanol-induced hypoglycaemia is scarce and further research is needed to define evidence-based recommendations.

Excessive consumption of alcohol interferes with diabetes management and patients with excessive or risky alcohol consumption are less likely to implement therapy recommendations on exercise, nutrition, medication, blood glucose self-monitoring or regular HbA_1c monitoring. There is a linear relationship: the higher the alcohol consumption, the less frequently therapy recommendations are implemented.

According to the S2k clinical practice guideline "Psychosocial Factors and Diabetes", alcohol consumption should be assessed regularly – at least once a year – in people with diabetes, and help should be offered when risky alcohol consumption is an issue. [37, 121]

Nutritional supplements

Recommendation

• People with T1Dm should cover their nutritional needs with a balanced diet. Routine supplementation with micronutrients is not recommended.

Comment

According to the American and Canadian Diabetes Associations, there is no clear evidence that supplementation with vitamins, minerals (e. g., chromium or vitamin D), herbs or spices (e. g., cinnamon or aloe vera) improves metabolic control in people without underlying nutritional deficiencies, and it is not generally recommended to improve glycaemic control. Routine supplementation with antioxidants (e. g. vitamin E, C or carotene) is not recommended due to a lack of evidence of efficacy and long-term safety concerns. However, multivitamin supplementation may be necessary in special patient groups such as pregnant or lactating women, elderly individuals, vegetarians or people on an extremely low-calorie or low-carbohydrate diet [5]. Instead of the general recommendation of routine administration of dietary supplements, people with diabetes should be encouraged to meet their nutritional needs through a balanced diet [7].

There is data on polyunsaturated fatty acids (PUFA) supplementation for preclinical and clinical T1Dm [110], which has classified the evidence as "low" that PUFAs protect against preclinical T1Dm when interventions during both pregnancy and early life were combined [110].

A small cohort study of newly-manifested T1Dm showed an improvement in surrogate parameters of endogenous insulin secretion for a 12-month co-supplementation of n-3-PUFAs and vitamin D in the group of co-supplemented children vs. children supplemented with vitamin D alone, with a reduction in the nutritional intake of arachidonic acid against the background of a Mediterranean diet [111].

Serum concentrations of vitamin D are lower in patients with T1Dm than in controls [112] [113]. The effects of vitamin D supplementation on the risk of T1Dm in infancy/toddlerhood were investigated in 2 meta-analyses and a review [113] [114] [115]. According to observational studies, vitamin D administration in infancy/toddlerhood appears to be associated with a reduced risk of T1Dm [113] [114] [115]. A dose-response relationship could be subject to this relationship: a higher vitamin D intake is associated with a lower risk of T1Dm, and the timing of supplementation could also be decisive, a lower risk of T1Dm was found at 7–12 months vs. 0 and 6 months of supplementation [115]. Two observational studies also suggest that vitamin D administration in young adults may have a protective effect on the risk of T1Dm [113]. According to systematic surveys, the results of vitamin D treatment for manifest T1Dm are contradictory and vitamin D supplementation only shows a protective effect on β-cell function and glycaemic control in some studies [113] [116] [117]. The current recommendation for vitamin D is that people with a high genetic risk for T1Dm should avoid and prevent vitamin D deficiency by adequate supplementation, however, the evidence is insufficient for the administration of higher doses of vitamin D [116].

In a case-cohort study of 257 children with T1Dm, the question was investigated whether iron supplementation during pregnancy and the first 18 months of life is associated with an increased risk of T1Dm in childhood. It was concluded that maternal supplementation with iron is not associated with the risk of T1Dm, but that supplementation in babies/toddlers shows an inverse association with the risk of T1Dm [118].

Serum concentrations of the trace elements chromium, zinc and magnesium are lower in persons with T1Dm compared to control persons. Observational studies show correlations between lower serum concentrations of these trace elements and poorer glycaemic control in subjects with T1Dm, so that supplementation may help improve metabolic control. However, further studies are needed to formulate a clear recommendation [119]. For the trace element zinc, a further systematic review, a meta-analysis, and a review were identified. The former comprises 25 studies, 3 of them with patients with T1Dm. The 2 case-control studies show an increased zinc concentration in erythrocytes as well as reduced lipid peroxidation after zinc supplementation, and the randomised, double-blind study demonstrates an effect of zinc supplementation on lipid metabolism [120]. A review describes zinc supplementation as a possible measure to improve blood glucose control and lipid metabolism in individuals with T1Dm, but points to the need for further studies due to the conflicting results of existing human studies [119].

Probiotics

Recommendation

• In view of the current study situation, no recommendation can be made for taking probiotics for the prevention or therapy of T1Dm mellitus.

Comment

The intestinal microbiome and the immune system are closely intertwined [122]. The immunomodulating effect of the intestinal microbiota or its metabolites, such as short-chain fatty acids, especially butyrate, is shown, among other things, by their effect on regulatory T cells [123] [124], the inflammatory status [123], and the function of the intestinal barrier [125]. In several studies of participants with diagnosed T1Dm, microbial diversity was found to be lower than in healthy participants [126] [127] [128]. In the period immediately before or at the onset of beta-cell autoimmunity, a higher proportion of Bacteroides was repeatedly observed in the subjects compared to the control group [129] [130] [131] [132]. Current studies suggest an association between reduced production of short-chain fatty acids, especially butyrate, by the microbiome, and an increased risk of T1Dm [126] [132] [133]. To examine the extent to which probiotic supplementation has a preventive effect on the development of beta-cell autoimmunity, for example, the prospective, longitudinal, multicentre cohort "Environmental Determinants of Diabetes in the Young" (TEDDY) surveyed probiotic supplementation pre- and postnatally in 7473 infants/children with a genetic predisposition to T1Dm. Early infant (0–27 days postnatal) probiotic intake may reduce the risk of beta-cell autoimmunity in children with high-risk genotype (HLA-DR3/4) [134]. On the other hand, in a double-blind, randomised, controlled trial, the administration of probiotics in infancy was not associated with the development of beta-cell autoimmunity [135].

In addition to preventive research on beta-cell autoimmunity, there are also studies on the effects of probiotics in already manifest T1Dm. An eight-week supplementation of synbiotics (Lactobacillus sporogenes GBI-30 with maltodextrin and fructooligosaccharides) in 50 subjects (4–18 years old) with diagnosed T1Dm resulted in an improvement in fasting blood glucose, HbA_1c, high-sensitivity C-reactive protein (hs-CRP) and total antioxidant capacity (TAC) [136].

There is also the following to consider with probiotic supplementation: On the one hand, probiotics may exhibit antibiotic resistance in mobile genes that can be transferred to other, possibly pathogenic bacteria through interbacterial exchange [137]. The investigation of various commercially-available probiotics showed that the probiotic bacteria tested were resistant to several different broad-spectrum antibiotics [138]. On the other hand, in rare cases, a weakened intestinal barrier function in critically-ill patients can lead to a translocation of the supplemented microorganisms [139].

German Diabetes Association: Clinical Practice Guidelines

This is a translation of the DDG clinical practice guideline published in Diabetologie 2024; 19 (Suppl 2): S236–S250.DOI: 10.1055/a-2311-9952

Conflicts of interest

D. Rubin: Lecture fees: DGVS and Kaiserin-Friedrich-Stiftung. A. Bosy-Westphal: none. S. Kabisch: fees and travel expenses by Sanofi, Berlin Chemie, Boehringer Ingelheim and Lilly; Travel expenses and research funding by J. Rettenmaier & Söhne, Holzmühle; further research funding by Beneo Südzucker and California Walnut Commission. P. Kronsbein: none. K. Müssig: none. MC. Simon: none. A. Tombek: none. K. Weber: none. T. Skurk: Lecture fees: Novo Nordisk.

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Publication History

Article published online:
06 May 2025