In addition to a generally lower calorie diet, a limited intake of the amino acid methionine could also contribute to the prevention of type 2 diabetes. This is shown by a mouse model study from a research team at the German Institute of Human Nutrition (German: Deutschen Institut für Ernährungsforschung or DIfE).
Methionine is a sulfurous, essential amino acid that cannot be produced by the body itself. Methionine is required for the formation of neurotransmitters and hormones, among other things. The amino acid is mainly found in meat and fish, dairy products and eggs - and in smaller amounts in nuts. Since vegetables and fruits contain hardly any methionine, a plant-based vegetarian or vegan diet is usually low in methionine compared to a diet based on meat and fish.
In earlier studies, the research team of the Department of Experimental Diabetology at DIfE observed that mice fed low-protein food gained less weight, had improved glucose tolerance, and consumed more energy than animals fed standard food.
The researchers were now able to show that diabetes-prone mice on a nine-week low-methionine diet had a significantly improved glucose metabolism and a higher insulin sensitivity than those on the same diet with a higher methionine content, despite having the same protein and high-fat content. This effect was independent of body fat content, which was not significantly different in both groups at the end of the study. The positive effect of methionine reduction could be reversed by the addition of cysteine to the diet.
Teresa Castaño-Martinez and her team of researchers have also discovered the possible mechanisms by which the positive effect on glucose metabolism is mediated: With reduced methionine uptake, the liver apparently releases more fibroblast growth factor 21 (FGF21), which in turn seems to lead to higher serum adiponectin levels. In addition, thermogenic genes were upregulated in the subcutaneous white adipose tissue, which suggests an increased formation of brown adipose.
In a further part of the study, the researchers investigated whether a vegetarian (and thus methionine-poor) diet also leads to higher FGF21 levels in humans. They were able to show that vegans and vegetarians actually have significantly higher FGF21 plasma levels than people with a mixed diet containing meat. If people with a mixed diet were to follow a vegetarian or vegan diet, an increase of FGF21 could be observed after only four days. The increase was even higher for vegan diets than for vegetarian diets. This could explain why vegans and vegetarians have a significantly lower risk of type 2 diabetes.
It would now be important to find out to what extent a reduced methionine intake actually contributes to an increase in FGF21 levels in humans. In the future, the research team intends to carry out investigations with vegans in order to uncover additional indications for the possible involvement of methionine in the development of type 2 diabetes.
If the results are also confirmed in humans, this could be of great importance for the prevention and treatment of type 2 diabetes. It is possible that people do not have to constantly count calories or generally do without protein-rich foods - the reduction of methionine might be sufficient. It may also be sufficient to take a vegetarian week every now and then to raise the FGF21 level. This could significantly increase the chances that diet regimes are acceptance by different types of patients.
Source:
Teresa Castaño-Martinez et al; Methionine restriction prevents the onset of type 2 diabetes in NZO mice; FASEB Journal (2019); DOI: https://doi.org/10.1096/fj.201900150R