by Valeria Montani
How does this dietary intervention aimed at supporting the normal alternation of day and night work? The various models of intermittent fasting. I study
I’ve read that intermittent fasting can help prevent type 2 diabetes: right?
Answers by Valeria Montani, Acting Director of the UOC Endocrinology and Diabetology Atri Hospital (TE), Association of Diabetologists (VAI AL FORUM)
Intermittent fasting is a dietary intervention, aimed at supporting the normal alternation of day and night (circadian rhythm) which regulates the functioning of the endocrine system, the autonomic nervous system and the metabolism of nutrients. There is also evidence, in laboratory animals, of its efficacy in preventing and treating metabolic pathologies, especially at the cardiometabolic level such as reduction of blood pressure, insulin resistance, adipose tissue and the onset of type 2 diabetes, stroke and heart disease. Even in humans, in healthy subjects, it seems effective in the prevention of the aforementioned pathologies.
How does intermittent fasting work?
But how does intermittent fasting work? Its mechanism starts from the physiology of digestion and insulin secretion. The food we eat is broken down by enzymes in our intestines into small molecules which, at the end of the digestion process, are absorbed, enter the bloodstream and arrive as nourishment in all body tissues. Carbohydrates, especially sugars and refined grains (such as white flour and rice), are broken down into glucose which is then released into the bloodstream and used by our cells for energy. When glucose is not used completely, the body does not waste it but stores it in adipose tissue, turning it into fat.
The role of insulin
The main actor of this fine mechanism is insulin, a hormone produced by the pancreas which is released into the circulation especially after meals, when glucose levels increase, and allows the glucose itself to enter the cells. Therefore, between meals, our insulin levels decrease and our fat cells activate the enzyme hormone-sensitive lipase, the main enzyme responsible for the degradation of triglycerides into fatty acids and glycerol (lipolysis). From fatty acids, ketone bodies are formed by the liver and are used as the main energy fuel for most body tissues. These are the premises for understanding that the purpose of intermittent fasting is to allow insulin levels to drop enough and long enough for the body to burn stored fat and promote autophagy.
Various models of fasting
Research has experimented with various intermittent fasting models, i.e. dietary patterns in which periods of free eating alternate with periods of complete or almost complete fasting: in one of the models used 8/16, the meals are concentrated in 8 hours while in the rest of the day fasting is carried out; another model, called 5-2, greatly reduces the calories eaten on two days of the week (about 500 calories per day), while in the remaining 5 days the diet is free. Another is fasting every other day: one day with free food is followed by one with a maximum intake of 25% of caloric needs. However, a Mediterranean-type diet is always advisable in the free diet phases.
Pilot study
A pilot study, recently published in the journal Cell Metabolism, evaluated for the first time the effects of intermittent fasting on 19 people with metabolic syndrome, a condition characterized by insulin resistance and the association of at least three factors including obesity, high and high levels of fat (cholesterol, triglycerides) and fasting blood sugar, burdened by a high risk of type 2 diabetes mellitus and cardiovascular disease.
13 women and 6 men with metabolic syndrome, mostly obese, limited their food intake to 10 hours a day with fasting for the rest of the day for 12 weeks, with no indications to reduce their total caloric intake or modify their their diet, nor their level of physical activity. At the end of the 3 months, participants lost an average of 3.3 kg, with significant reductions in body mass index, body fat, visceral fat, and waist circumference. Positive effects have been found on cardiometabolic parameters, with reduction of blood pressure, total cholesterol, LDL cholesterol, independently of weight loss.
11 participants had a form of pre-diabetes (glucose ≥100 mg/dl and/or glycated hemoglobin ≥5.7%), one participant was affected by type 2 diabetes: in this subgroup the dietary intervention led to a significant reduction of fasting blood sugar and glycated hemoglobin, particularly marked in subjects with diabetes.
Effective to treat metabolic syndrome?
The study concludes that intermittent fasting, by inducing a regular cycle of eating and fasting and supporting the physiological circadian rhythm of our body, could be an effective strategy in the treatment of metabolic syndrome and therefore in reducing the risk of type 2 diabetes mellitus and cardiovascular diseases associated with it, with a higher level of adherence than continuous caloric restriction and increased physical activity, however desirable. This is an interesting study, but small in size and limited follow-up. At the moment, the preliminary results are encouraging. However, there are still several aspects to be clarified, starting with the long-term effects, adherence and efficacy of this food model. Finally, some practical aspects still need to be understood, such as what is the best time slot to concentrate meals and what the personal and social consequences of this type of diet might be.
July 7, 2023 (change July 7, 2023 | 09:32)
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