Get fat for the benefit of science
Volunteers ate six thousand calories a day to help identify the causes of diabetes
Margarita Paimakova, Vesti
Obesity is one of the risk factors determining the propensity to develop type 2 diabetes, but researchers are still not sure what the reason for this relationship is. Now a team of scientists has asked volunteers to consume 6 thousand calories daily in order to find some clues.
Excessive food intake causes a lot of problems, and obesity is just the tip of the iceberg. The consequences of overeating can include the risk of diabetes, heart disease, and even some cancers, although no one is still exactly sure why.
Resistance to the hormone insulin probably plays a role. When a healthy person takes food, glucose levels rise, and the body reacts by producing insulin. This hormone causes the body to absorb excess glucose, but if a person develops insulin resistance, this does not happen. Therefore, after eating, the blood glucose level remains high for a long time, and this can lead to damage to the kidneys, nervous system and heart.
Guenther Boden and Salim Merali from Temple University in Philadelphia, together with their colleagues, decided to study exactly how overeating can lead to insulin resistance. As a result, they fed six healthy male volunteers 6 thousand calories of food every day for a week - this is twice their usual daily norm (healthy men aged 30 to 50 years should eat about 2,200 calories daily).
"In fact, it was an ordinary "American" diet consisting of pizza, burgers and other similar foods," says Merali – Each of the volunteers remained in the hospital throughout the experiment, where we carefully protected them from any kind of physical activity: 6 thousand calories is a lot, but some athletes consume just that the amount during intensive training."
It is not surprising that the volunteers began to gain weight: by the end of the week, each weighed about 3.5 kilograms more than at the beginning of the experiment. On such a diet, all volunteers acquired insulin resistance within two days: in fact, they all earned diabetes.
To find an explanation for this, Boden and Merali tested several theories. One of them suggested that molecules called free fatty acids, which are apparently elevated in the blood of people with insulin resistance, can trigger resistance to the hormone. However, its levels were normal for volunteers. The participants also did not have elevated levels of those compounds that cause inflammation – this allowed them to reject the second theory.
Instead, a daily urine test helped to identify another "culprit". The team of scientists noticed that a large number of lipid oxidation compounds were observed in the samples of volunteers during the week, which are formed due to the fact that reactive oxygen species attack cell membranes.
Compounds are a distinctive feature of oxidative stress occurring in the body. The team then identified signs of this stress by biopsiing the adipose tissue of the volunteers. Boden believes that this is how the process that ultimately leads to insulin resistance is triggered.
Most likely, the oxidative stress caused by overeating makes it difficult to regulate blood sugar, as it alters the structure of the protein that is usually responsible for the removal of glucose from the blood. Insulin sends the same signal, but glucose is not removed from the blood.
However, it is quite possible that oxidative stress is only one of the important factors in the acquisition of insulin resistance – it is quite possible that other mechanisms are involved in the process. Overeating also leads to the accumulation of fat in the muscles and liver.
Boden hopes that in the future oxidative stress and modified protein can become a target for therapy against diabetes. Probably, adding antioxidants to high-calorie foods will help limit its health effects.
Details about the effect of a high-calorie diet on insulin levels were published in the journal Science Translational Medicine (Boden et al., Excessive caloric intake acutely causes oxidative stress, GLUT4 carbonylation, and insulin resistance in healthy men).
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11.09.2015