Prevention of T2DM: nutritional aspects
Diet plays a central role in the development of type 2 diabetes. Two aspects of dietary intake have to be considered: one is the composition of the diet and the other is the amount of energy intake. Both may have independent and additive effects on the risk of diabetes. Compared to diet composition obesity is a much stronger promotor of diabetes development.
Numerous observational studies over the last decades in both men and women have repeatedly demonstrated that a Western-style diet characterized by energy-dense foods increases the risk of developing type 2 diabetes. It became particularly clear that a high-fat diet low in fiber content promotes a chronic positive energy balance leading to overweight and in those at genetic risk to type 2 diabetes .
More than two decades ago, intervention trials were initiated to investigate the effects of lifestyle intervention programmes on the clinical manifestation of type 2 diabetes in persons at increased risk characterized by impaired fasting glucose (fasting plasma glucose of 100 to 125 mg/dl) or impaired glucose tolerance (2-hour glucose level after an 75 g oral glucose load between 140 and 199 mg/dl and fasting glucose < 126 mg/dl). In the Finnish Diabetes Prevention Study and the American Diabetes Prevention Program the recommended lifestyle intervention components were very similar
- Weight loss by 7 %
- Total fat intake < 30 % of total energy intake
- Saturated fat intake < 10 % of total energy intake
- Fiber intake > 15 g per 1000 kcal
- Physical activity > than 150 min/week
Both studies reported a decrease in the incidence of type 2 diabetes by 58 % after an average duration of intervention of 3 years. In the Indian diabetes prevention programme, a risk reduction of 28.5 in participants with IGT vs. the control group after a mean duration of intervention of 30 months. Modification of the diet included a reduction in total calories, refined carbohydrates and fats, avoidance of sugar, and inclusion of fiber-rich foods . In the Chinese Da Qing study, the dietary intervention resulted in a reduction in the incidence of type 2 diabetes by 31 % after an intervention period of 6 years . It is noteworthy that the clinical benefit was maintained in all studies for many additional years after discontinuation of active intervention, which may be explained by a metabolic memory effect and/or sustained changes in lifestyle.
In addition to these well-evaluated and confirmed dietary concept, a recent report from the PREDIMED Study Group in Spain demonstrated that a mediterranean type of diet is also suitable to lower the risk of developing type 2 diabetes. In a subgroup of people aged 55 to 80 years, Mediterranean diets without caloric restriction were effective to reduce the incidence of diabetes by about 50 % after 4 years compared to a low-fat diet . These diets were also found to reduce cardiovascular events in people at high cardiovascular risk indicating a dual action of the Mediterranean diet.
Concerning the effects of single dietary components a subanalysis of the Finnish Diabetes Prevention Study provided some remarkable insights. It turned out that the hazard ratios for diabetes incidence during a mean follow-up of 4.1 years were 0.38 for the highest vs. the lowest quartile of fiber intake, 2.14 for the highest quartile of fat intake, and 1.73 for the highest quartile of saturated fat intake vs. the lowest quartile . Thus, dietary fat and fiber intake are single diet components with significant effects on the progression to type 2 diabetes in high-risk subjects.
Apart from the composition of the diet it is rather obvious that weight reduction by any means is resulting in a risk reduction for diabetes. The usually preferred dietary approach to achieve weight loss is a combination of an energy-restricted balanced diet and an increase in physical activity. Although this strategy has turned out to be a rather effective in preventing type 2 diabetes in subjects at risk. However, it has to be considered that type 2 diabetes in those prone to the disease e.g. by their genetic predisposition cannot be fully prevented. This was convincingly shown by the Swedish Obese Subjects (SOS) Study. Substantial weight loss by bariatric surgery was found to delay the onset of the disease by many years, but could not definitely prevent diabetes . In a recent analysis of the 15-year follow-up data, the incidence of type 2 diabetes in the subjects undergoing bariatric surgery was reduced by more than 70 % compared to the subjects receiving conservative treatment without significant weight change (6.8 cases vs. 28.4 cases per 1000 patient years). There is still a proportion of subjects at risk who are “non-responders” to any type of intervention which is still poorly understood.
Other dietary concepts may also promise some protection against diabetes development. Moderately low-carbohydrate diets characterized by 30 – 40 % of calories from carbohydrates, 40 % from mono- or polyunsaturated fats and 20 to 25 % from protein were found to improve glucose tolerance and lipid metabolism. However, intervention studies to prove this concept are still missing, but are required to derive solid recommendations.
In conclusion, a growing bulk of human studies suggest that various dietary strategies are available to lower the risk of developing type 2 diabetes. The following components should be considered: - in case of overweight/obesity weight loss is the most powerful intervention - a low intake of saturated fat (< 10 % of total calories) - a high fiber intake (> 15g/1000 kcal) preferentially from whole-grain products - as an alternative a Mediterranean diet
Note: the greater the weight loss in association with these diets the greater is the protection from type 2 diabetes. For practical terms, any dietary recommendations should consider the individual situation including the wishes and capacities of the individual subject. In addition, education and care by health professionals is urgently recommended to protect the individual from potential adverse consequences and to secure optimal health benefit.
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