An important review on fasting diets has recently been published in Gut magazine. In recent years, several studies have been performed with various diet manipulation schemes to optimize metabolic health. There are two intervention strategies: periodic fasting, where food intake is greatly restricted during certain days and another in which the period of food intake is limited to a few hours of the day, remaining fasting the rest of the time (intermittent diet).
In relation to periodic fasting diets, there are two variants that are the most commonly used. One is the 5:2 diet which consists of 5 days of normal eating with no food restrictions and 2 non-consecutive days of fasting. The other is a continuous alternating pattern of eating and fasting days, in which an intake of up to 25% of the usual calories is sometimes allowed on fasting days, although the traditional way is to do total fasting on alternate days.
Benefits and effectiveness of intermittent fasting diets
Several studies in healthy volunteers have shown that periodic fasting diets induce beneficial effects (as compared to baseline) on fasting glucose, fasting insulin, cardiovascular markers, including LDL cholesterol (bad), total cholesterol, triglycerides and blood pressure. In addition, these diets are well tolerated, even for prolonged periods (6 months). Diets carried out for 8-12 weeks produce between 3-8% weight loss, with no differences between the 5:2 diet and the alternate day diet. It should be noted that the degree of weight loss with periodic fasting diets is equivalent to that obtained with classic continuous caloric reduction diets.
Regarding weight recovery when suspending diets, there are no differences between periodic fasting diets and calorie restriction diets (in both cases around 30% of the weight loss are recovered in the first 6 months).
Evaluation of intermittent fasting diets: health effects and considerations
Periodic fasting diets do not produce gastrointestinal symptoms, fatigue, irritability or dizziness as occurs with calorie-restricted diets. However, the application of periodic fasting diets in patients with diabetes treated with insulin or hypoglycemic drugs can produce episodes of hypoglycemia (especially in these cases, these diets should be done under medical supervision).
In intermittent diets, unrestricted food intake is allowed for a few hours a day and the rest of the time only water can be taken. In most of the studies carried out, the allowed period of food intake is 6 to 10 hours a day. This intake rate is well tolerated and effective (periods shorter than 4 hours or longer than 12 hours are not effective). The intermittent diet induces a 3-4% weight loss, lower than that obtained with periodic fasting diets (3-8%) and calorie restriction diets (5-7%).
For all of the above, the most effective diet for weight loss is periodic fasting, followed by caloric restriction and finally intermittent diet.
Dr. Carreño and the doctors from the Foundation apply these concepts in the treatment of patients with fatty liver due to excess weight.