Protocollo di ricerca
The research protocol has been written for medical doctors, researchers and people who want to know more about the scientific background of 'The food hourglass'.
Remark: this protocol has specifically been written for type 2 diabetes patiens. However, the foodhourglass can be used by anyone who wants to live healthier and reduce the risk of aging-related diseases (like diabetes).
A novel concept for nutrition guidance in type 2 diabetes and weight loss
Currently, patients diagnosed with type 2 diabetes are advised to follow dietary guidelines issued by national organizations, like the American Diabetes Association (ADA) or the National Institute for Health and Care Excellence (NICE). However, the health benefits that are brought about by these recommendations are rather modest. For example, patients following the American Diabetes Association guidelines reduce on average their HbA1c with 0,4% (1). Yet there exist various diets that could have a more substantial health impact. For example, a more vegetarian oriented diet for diabetes patients is three times as effective in reducing HbA1c compared with patients following the ADA diet guidelines (1). A low glycemic index diet made it 75% less likely to increase diabetes medication than when following an ADA diet (2). A hypocaloric mainly vegetable based diet can even reverse diabetes in all subjects in 8 weeks time (3). These and similar studies show that nutrition can substantially impact diabetes. However, providing diet guidelines that can be adhered to by patients in the long term and that can change often deeply rooted eating habits are not easy to implement.
We developed the food hourglass, a nutrition model to help type 2 diabetes patients to make healthier food choices, in order to improve their metabolic and cardiovascular health and lose weight. The food hourglass is an alternative to a low fat or low carb/high protein diet for diabetes patients. With the food hourglass we want to introduce a new type of diet, called a low glycemic load healthy macronutrient diet (HMD).
The food hourglass is a figure in the shape of an hourglass (2 triangles facing each other), with in the top triangle containing food of which the intake should be reduced, while the bottom triangle contains food of which the intake should be increased.
Figure 1. The food hourglass
Each colored layer in one triangle has a corresponding colored layer in the opposite triangle so that patients can easily see how to replace one food by another healthier alternative. For example, red meat in the red layer in the top triangle can be replaced with poultry or fish in the corresponding red layer in the bottom triangle.
The food hourglass draws on insights from diverse fields like endocrinology, biogerontology, evolutionary medicine and nutrition science. The food hourglass emphasizes a substantial reduction of specific starchy foods (temporarily or indefinitely). These starchy foods (SFDs) are bread, potatoes, pasta and rice. Similar recommendations can be found in the Harvard food pyramid, the Mayo Clinic food pyramid and the official Austrian and Swiss food pyramid. These food models put much less emphasis on starchy foods like (whole grain) bread, potatoes or rice. For example, the base of the Mayo Clinic Food Pyramid and Austrian food pyramid (originally composed of bread, potatoes, pasta and rice) is completely replaced by vegetables and fruits. Potatoes have been moved to the off limit top of the Harvard food pyramid (together with red meat), next to soda and sweets.
The rationale behind these changes is that low glycemic index (GI) and low glycemic load (GL) diets can reduce the risk of metabolic diseases like cardiovascular disease and type 2 diabetes. For example, a prospective study following 15 714 women for 9 years showed that the highest quartile of dietary glycemic load was associated with a 47% increased risk compared to the lowest quartile, further increasing to 78% for overweight women (4). A high glycemic load and low fiber diet was associated with a doubling of the risk of type 2 diabetes (N = 43 000; RR 2,17) (5). A prospective study following a cohort of 75 521 women for 10 years showed that the risk of coronary heart disease for the highest glycemic load quintile was 98% higher (6). A prospective study of 64 227 Chinese women for 4,6 years showed a correlation between glycemic index, glycemic load and type 2 diabetes, especially for the glycemic load and rice intake (7).
Additionally, studies have shown that low glycemic index diets are superior to low fat diets in terms of improving cardiovascular parameters and weight loss. A Cochrane meta-review showed that ad libitum low glycemic index diets are superior to caloric restricted low-fat diets in terms of lipid profiles and weight loss (8). Adhering to a low glycemic index diet improves metabolic parameters more than an isocaloric low fat diet (challenging the assumption that a calorie is always a calorie) (9). A hypocaloric mainly vegetable based diet without bread, potatoes, pasta and rice can reverse diabetes in 8 weeks time3.
In the food hourglass, we do promote the use of one particular grain product, namely oatmeal, which can serve as a substitute for bread, especially during breakfast. Oatmeal has a lower glycemic index that white and brown bread, contains oat fiber (water soluble beta-glucans) that have a beneficial impact on cholesterol and glucose levels. In contrast to whole grain bread, oatmeal has been granted health claims by the European Food Safety Authority (EFSA) and can convey benefits to diabetes patients. Diabetes patients with difficult to regulate glucose levels who were put on a 2 day oatmeal diet, were able to reduce their insulin medication by 40%, an effect that lasted for at least 4 weeks after this intervention (10). Using oatmeal instead of higher glycemic index cereals and bread, resulted in lower blood sugar levels in type 2 diabetes patients (11).
The food hourglass recommends patients to replace bread and cereals with oatmeal during breakfast, and to replace potatoes, pasta and rice with legumes (beans, lentils, peas, …), mushrooms and an extra portion of (other) vegetables for lunch and dinner. A study among 1879 adults showed that substituting one serving of beans for one serving of white rice was associated with a 35% (95% CI: 15%, 50%) lower risk of the metabolic syndrome (12). The food hourglass advocates vegetables, legumes, oatmeal and fruit as basic bulk foods to improve blood sugar levels and to attain healthy weight loss.
Besides the reduction of starchy high glycemic load foods, the food hourglass recommends replacing read meat more often with white meat and fish. This because an increased intake of red meat is associated with an increased risk of cardiovascular disease, diabetes and cancer (N= 120 000) (13). A 12 year follow-up study of 27 147 individuals showed a direct correlation between meat intake, total protein intake and type 2 diabetes (14). A study with almost half a million Europeans showed a 44% increase in mortality in people who ate more than 160 grams of processed meat a day compared to 10-19,9 grams per day (15). Substituting red meat with healthier protein sources like chicken reduces mortality with 14% (13). Increasing the intake of fish, especially fatty fish, is associated with reduced cardiovascular mortality and improved cardiovascular parameters (16). Red meat can also be replaced with tofu (soy) and quorn (a protein-rich food product made of a fungus).
Regarding diary, cheese is the only diary product that is recommended, being an important source of menaquinone (vitamin K2) and trans-palmitoleic acid in the western diet. Milk is not recommended because of the insulinotropic effects of milk (17,18) and other possible negative health effects of milk in the long term (19–21). Soda and other sugar-sweetened beverages are advised against (like commercial low-fiber fruit juice). Ample amounts of water, and further tea, alcohol in moderation, low-sugar vegetable milk and coffee are healthier drink alternatives. The food hourglass further advocates healthy snacks (like nuts, dark chocolate, soy yoghurt, fruit, legumes, …) and the use of healthier sugar substitutes (like stevia, tagatose, sugar alcohols and other compounds that result in reduced sugar and insulin increments) and healthy vegetable fats.
It’s well known that it’s often difficult for patients to adhere to dietary guidelines, especially in the long term. The food hourglass can make long term compliance more likely and could provide more pronounced health benefits for type 2 diabetes patients compared to low fat diets and low carb/high protein diets.
Firstly, a model shaped like a food hourglass can make a more clear distinction between food products that are recommended (in the lower triangle) and food products that should be used less (in the upper triangle). Additionally, the corresponding similar colored layers in both triangles clearly provide alternatives for the dissuaded foods.
While we do put limits on portions for certain foods (like alcohol, chocolate or meat: see further details below), we want to keep the dietary guidelines as clear and simple as possible. We deliberately don’t want to encumber patients with calorie counting, calculating protein or fat content or weighing foods, methods that can reduce compliance in the long term. As studies show, low glycemic index and glycemic load diets negate the need for calorie restricted diets: patients can follow ad libitum low GI/GL diets and still lose weight and improve cardiovascular parameters (8).
The food hourglass models enables patients to quickly see and understand some important dietary principles (less high glycemic load foods, more healthy protein sources, more healthy fats), while at the same time providing clear alternatives that can direct them to healthier food choices. In this way, the food hourglass can also be very useful for medical practitioners in a clinical setting, when they need to provide dietary advice but only have a limited amount of consultation time.
Regarding the content of the food hourglass, the model not only incorporates the hypothesis that an increased intake of specific fats increases the risk of cardiovascular disease and weight gain, but also includes the more recent hypothesis that high glycemic load diets are also involved in metabolic diseases and overweight (22). Contrary to low-carb/high protein or low-fat diets, the food hourglass doesn’t advice against or favors specific macronutrient (carbs, fats or protein). Instead, it recommends the use of more healthier foods in each macronutrient group, namely low glycemic index/load carbohydrates, healthy protein sources (fish, poultry, vegetable protein, …) and healthy fats. We call this diet a low glycemic load healthy macronutrient diet (HMD), that can serve as an alternative to low-carb/high protein and low-fat diets.
In conclusion, the food hourglass wants to empower patients to make healthier food choices by providing a model that quickly and clearly explains some important dietary principles to attain weight loss and improve metabolic markers.
“The food hourglass: a low glycemic load healthy macronutrient diet (HMD) and nutritional model for nutrition guidance in type 2 diabetes.”
Adherence of type 2 diabetes patients to a fiber-rich low glycemic load healthy macronutrient diet (HMD) that involves the following guidelines (a strict interpretation of the food hourglass).
Duration of the study
8 weeks or 6 months.
Primary outcome measures
Secondary outcome measures
Tertiary outcome measures
Patients will be provided with a full-color illustration of the food hourglass and a set of recipes and follow-up consultations.
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