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Nutrition

The dangers of fasting

Staying a long time without eating may cause serious imbalances in the organism

EDUARDO CESARThink twice before going hungry during the week in order to be able to overindulge your appetite with a feijoada [pork and black bean stew] on Saturday. There are now indications that staying a long time without eating and then stuffing yourself may not be very healthy. Studies with animals have shown that prolonged fasting, alternating with over-feeding, may alter the functioning of insulin, the hormone that facilitates the entry and metabolism of glucose in the cells, and thus favor the development of diabetes.

The warning comes following a study carried out by nutritionist Fernanda Cerqueira for her PhD thesis at the Chemistry Institute at the University of São Paulo (USP), supervised by Alicia Kowaltowski. Fernanda suspected that diets that restrict food consumption might have different effects on the organism, even though they all lead to weight loss. As it is extremely difficult to carry out this type of study on people Fernanda submitted some 100 rats to diets with various restrictions over a nine-month period, the equivalent of almost 20 years of the life of a person. She divided them into four groups: a control group, where the rats could eat as much as they wanted; one with calorie restrictions, which received 60% of the standard diet, plus supplementary vitamins and mineral salts; a group that was completely restricted, which received a 60% smaller diet, with no vitamin supplements; and the intermittent diet group, feeding only every other day.

The biggest surprises appeared in animals on the intermittent diet. After a day of fasting they were starving and ate twice as much as the control group rats all in one go. They also lost weight, but just muscle mass; the amount of abdominal fat remained the same as in the control group. Likewise, the animals that fasted absorbed glucose, but took less advantage of it. The probable explanation is the accumulation of free radicals, comprising fairly reactive chemicals that were found in greater quantities than in the animals in the control group. The animals that fasted every other day had eight times more hydrogen peroxide, a highly reactive compound. Peroxide is a molecule derived from superoxide radicals that are involved in forming peroxynitrite, which adheres to a molecule called an insulin receptor. In its turn the receptor activates other molecules and helps the glucose enter the cells.

“The insulin still binds with the receptor, but the response of the receptor is less than normal,” says Fernanda, according to whom the reaction of the peroxynitritye with the insulin receptor is an irreversible phenomenon and the consequence is that the cells, particularly muscle cells, will receive and metabolize less glucose than they need. “Even though they weighed less, the rats submitted to the intermittent diet lost the suitable metabolic regulation,” says Alicia. “The effects of frequent fasting should be investigated in more depth in human beings too.”

Sedentary pattern
The results obtained with laboratory animals cannot be simply transposed to human reality. The first reason is that the animals in the control group may not be the ideal standards for delimiting the results. In 2010, in PNAS, researchers from the United States showed that vivarium rats, because they eat how much and when they want and are sedentary, are insulin-resistant, have a predisposition to inflammation and weigh 20% more than the wild animals.

“The laboratory animals used as a control in a lot of biomedical research correspond to a normal sedentary animal and not a normally active animal,” says Francisco Laurindo, a researcher at the Heart Institute of the School of Medicine at USP. Even so, the human organism obeys a logic that is similar to that of rodents, which suggests that the phenomena observed and their effects are also likely to be similar. “Restricting calories may function as a small stress factor, preparing the organism for a subsequent, more intense stressful situation,” says Laurindo.

Diets with restricted foods may also help people recover from illnesses and lessen the effects of excessive amounts of medication. Anyone who has had a heart attack has to take many drugs and follow a diet that restricts the consumption of fatty foods, one of the causes of cardiac problems. Laurindo’s group found an alternative: the Mediterranean diet, based on greens, vegetables, fruit and olive oil as the main source of fat. In a study on 19 people who followed the traditional diet and 21 the Mediterranean diet, the two diets reduce weight and improve blood pressure and other indicators of cardiac problems. “The difference,” he says, “is that the Mediterranean diet is tastier and allows for moderate consumption of cheese, olive oil and wine.”

A nutrition graduate from Goiânia and currently at Boston University’s School of Medicine in the US, Fernanda also suspected the diets that recommended that people eat a little every three hours. She thought that this strategy could keep the insulin and glucose at high levels, but the experiment with the rats made her rethink her ideas. “Fasting and then eating a lot can lead to a nutrient overload and peaks of insulin and free radicals.” Excess calories may result not only from food but also from beer, wine and other weekend pleasures. “Cells don’t distinguish the source of the calories, which may also come from alcoholic drinks.”

Scientific articles
CERQUEIRA, F.M. et al. Long-term intermittent feeding, but not caloric restriction, leads to redox imbalance, insulin receptor nitration, and glucose intolerance. Free Radical Biology and Medicine (forthcoming).
THOMAZELLA, M.C.D. et al. Effects of high adherence to Mediterranean or Low-Fat Diets in medicated secondary prevention patients. American Journal of Cardiology (forthcoming).

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