CD and CRHP dietary patterns
The meal kits will be produced and delivered twice weekly by an established company specialising in meal kit delivery services (Skagenfood A/S, Strandby, Denmark). The eucaloric diets, provided free-of-charge for 12 months, cover more than two-thirds of the total individual estimated daily energy requirements for body weight maintenance (~20% for breakfast, ~35% for dinner and ~10% for snacks). To allow for options and flexibility, participants will be responsible for lunch (~35% of total daily energy intake) while still required to adhere to the macronutrient distribution. Lunch and dinner can be interchanged if deemed necessary, for example, when going out for dinner, further enhancing adaptability of the diet to daily life.
The CRHP/CD diets comprise 30/50 E% from carbohydrate, 40/33 E% from fat and 30/17 E% from protein (table 1). To meet most energy needs, both diets have three calorie levels (2100, 2500 or 2900 kcal) not differentiating in the quality of carbohydrate, protein and fat except minor differences reflecting the overall difference in macronutrients found naturally in foods. Participants are assigned to the calorie level that matches their estimated energy requirements more closely, thus allowing for ad libitum dieting by changeable serving sizes and individual needs and preferences. The design of the diets, especially the three calorie levels, dietary patterns and macronutrient distribution ranges for carbohydrate, protein and fat is based on results and experience from previous studies.12 13
Macronutrient composition and quality of a conventional diabetes (CD) and a carbohydrate-reduced high-protein (CRHP) diet
Meal plans
The meal plans reflect a healthy eating pattern, taking cultural and sustainable choices into consideration, rotating every 3 weeks, repeated over the entire 12-month trial period, additionally changing ingredients throughout the seasons. Culturally appropriate substitutes for specific ingredients are made available with ethnic groups in mind, although optional for all participants.
Recipes are created by dietitians and chefs in accordance with the recommended calories and macronutrients; hence participants are advised not to add other ingredients to their meal, except various listed spices. However, preparation and cooking methods are optional, provided that all ingredients are used, making the meals adjustable for different lifestyles and individual preferences. An overview of meals along with examples and pictures are provided in online supplemental table S1 and figures S2 and S3, respectively.
Satiation, servings and portion sizes
Emphasis is on recognising the feeling of satiation and not overeating, which for many can be troublesome. Participants are instructed to eat every meal until they feel satiated, without trying to finish the entire serving if there is too much food. If a meal serving contains too much food, participants are instructed to eat an equal amount of each part of the meal, for example, two-thirds of the meat, two-thirds of the vegetables and two-thirds of the side dish. Participants must consider this before they start eating, to avoid eating, for example, all meat or salad. Advice is given to begin by portioning the serving, and start eating one portion first, for example, half of the prepared food, continuously assess hunger, and decide whether to eat the remaining portion or perhaps halve it again. Meals are for participants only; if living with a partner or other cohabitants, advice is given on how to cook meals and dine together while adhering to the diet and ensuring the desired macronutrient distribution.
Participants who consistently experience that they receive too much or too little food in the meal kits will be assigned to a different calorie level if possible or instructed to either increase or decrease the serving size, swap with another meal with a different calorie content or combine, for example, different snacks with or without breakfast or dinner.
Timing and frequency of meals
Timing or frequency of certain meals is flexible and adaptable, to align with individual preferences. Although a sufficient intake of calories with the advised macronutrient distribution at each meal is pivotal to assure satiety, participants are advised to avoid consciously restricting food intake or overeating, or eating ultra-processed hyperpalatable snacks.14 The provided snacks can be eaten at any time of the day.
Recipes
Besides the meal plan recipes, participants receive supplemental recipes, as well as seasonal and holiday recipes, supporting individual needs for serving sizes and reinforcing individual choices and adherence to the intervention (online supplemental table S2). The recipe booklet also includes a thorough introduction with nutrition information, cooking methods, measurement units, food storage tips, a list of shelf stable foods from the meal kits, macronutrient distribution and meal energy distribution. It was sought to keep the recipes simple, however, to ensure nutrient-dense meals consisting of many vegetables, beans, lentils and starchy vegetables, some recipes are somewhat laborious, estimating that overall 1–1.5 hours daily will be spent on cooking.
The meal plans can be different from what participants are familiar with, considering recipes, ingredients, meal frequency and timing, hence a period of adjustment is warranted. Participants must try all recipes and ingredients at least once, except if substitutions are necessary due to cultural or medical reasons. In such instances, or if participants develop strong aversion to certain foods, substitutes for these ingredients or dishes are found, however, participants need to purchase suitable substitutes themselves.
Excess food
Weighing all ingredients is important to ensure the correct macronutrient distribution. In the recipes, it will be specified whether to use excess food for example, meat, beans on another day. In case of leftover food, participants are instructed to either freeze or store it in the fridge, and use in other recipes, for example, lunch. Lunch recipes have been developed with this in mind. Many vegetables and fruits can also be pickled or preserved in other ways. This way, both participants and others can benefit from any excess food.
Drinks
Tap water and sparkling water with or without flavour are recommended as primary drinks. Coffee and tea with or without a little skimmed or low-fat milk, but without added cream or sugar, is allowed. Alcoholic beverages are permitted within the recommendations from the Danish Health Authorities, still taking the calorie and carbohydrate content into consideration. Artificial sweeteners are permitted, although avoiding artificially sweetened beverages as much as possible is recommended due to risk of sugar cravings for some individuals.15 Attention must be paid to the nutrition label when choosing such drinks, as some may still contain a significant number of calories.
Dietary adherence
By combining partial food provision by meal kits with monthly nutrition counselling and support from study staff, adherence to the diets is expected to be high. We aim to validate this quarterly by use of 3-day weighed food records, where participants record all foods and drinks, preferably weighed prior to consumption using a portable weighing scale (or otherwise estimated) into an electronic diet registration tool (MADLOG, Madlog ApS, Kolding, Denmark). Participants are advised to take photographs of the recorded foods and drinks to substantiate the food records. Furthermore, food frequency questionnaires and diet history interviews will be performed at the quarterly study visits, and dietary adherence evaluated by study staff and registered clinical dietitians (RCDs). Food records will be evaluated during the nutrition counselling sessions and advice will be given by RCDs on how to improve adherence when needed. If follow-up is deemed necessary, extra counselling or follow-up calls will be planned with participants. Additionally, adherence to assigned study diets will be assessed by analysing diurnal urinary excretion of urea, which is used as a surrogate marker for protein intake.
Nutrition education and counselling
After the allocated diet is revealed, participants receive their recipe booklet and a pamphlet with general information about nutrients. Hereafter, prior to the start of the intervention participants receive their first nutrition counselling (figure 1). All these sessions are conducted on an individual basis and held by RCDs. In the first session, the RCD collects nutrition assessment data along with diet history, explains dietary considerations and answers questions regarding the allocated diet. The next nutrition counselling sessions are scheduled 3 weeks after the first delivery of meal kits and monthly thereafter. Monthly counselling sessions will address how to adhere to the allocated macronutrient distribution, especially concerning the self-selected lunch meals, as well as how to navigate the food environment during, for example, holidays, weddings and birthdays. Importantly, as diets are expected to induce satiety, counselling will emphasise how to achieve the advised macronutrient distribution if participants cannot eat the planned serving size. Throughout the study, participants will give feedback on the meal kit recipes and, if necessary, specific food items can be substituted or other minor changes made to maintain a high degree of dietary adherence.
Overview of study visits, meal kit provision, nutrition education and counselling and evaluation of dietary adherence. For nutrition counselling sessions, attendance during first two sessions is preferred physical, thereafter virtual sessions or by phone are allowed. CD, conventional diabetes; CRHP, carbohydrate-reduced high-protein; FFQ, Food Frequency Questionnaire.
Changes in medication
Two experienced endocrinologists will be responsible for titrating the pharmacological treatment during the duration of the study, both of whom will be blinded to participants’ diet allocation. If possible, glucose-lowering medication will be kept constant during the entire study period. However, to ensure safety participants will be instructed to perform self-monitoring of blood glucose at home once weekly after the first 3 months of intervention. In the event of repeated fasting glucose levels >11.1 mmol/L or any diabetes-related symptoms (eg, fatigue, polyuria, thirst and confusion), participants will be referred to the study endocrinologists where necessary changes in medication will be assessed. To accommodate further safety concerns, if HbA1c levels are above 58 mmol/mol following 6 months of intervention, glucose-lowering medication will in most cases be intensified. The choice of therapy will be in accordance with current national guidelines as well as guidelines from the EASD and the ADA. During the study, if possible, all medications with known effects on lowering blood pressure and lipids will be kept constant. However, any cases of severe hypotension or hypertension, or hyperlipidaemia as judged by the study endocrinologists (from symptoms or routine measurements after 6 months), will be remedied by optimising pharmacological therapy. Of note, the treatment of participants with highly elevated blood pressure and lipids will be optimised prior to study enrolment.
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