Intermittent fasting: what is the most effective formula?

By David Clayton, Nottingham Trent University

Intermittent fasting is a type of diet that limits the amount of time allowed to eat. The appeal of these diets is that there is no need to count calories or eat certain foods. But this method has so many variants that it is difficult to discern which one is the best. Next we present what science says.

The 5: 2 diet

It is a popular variant of intermittent fasting consisting of maintaining a very low calorie diet (about 500 kilocalories) for two days a week (can be any two days) and eat normally the remaining five days.

Scientific studies have shown that the 5: 2 diet allows you to lose weight and also improves several health markers, such as reducing blood glucose and cholesterol levels. But, generally, this diet is no more effective for losing weight than traditional dietary methods. This is because the 5: 2 diet reduces calorie intake to a similar extent to traditional diets.

There are data that indicate that placing the two days in which very few calories are ingested consecutively can improve insulin sensitivity – a risk marker for type 2 diabetes – to a greater extent than the classic diet. In addition, compared to the traditional diet, this method involves a reduction in blood lipids (fatty substances found in the blood).

An important added advantage of the 5: 2 diet is that food can be consumed during the "fasting" period, which allows ingesting essential nutrients. Diets often lead to loss of bone and muscle mass, in addition to fat loss, since it is difficult to maintain a balanced diet and, at the same time, reduce calorie intake. This result can spoil the efforts invested in losing weight in the long term, since the muscle is metabolically more active (that is, it burns more calories) than fat. Eating enough protein can help stop the loss of muscle mass during the diet, with the added benefit of reducing appetite.

Fasting on alternate days

While the 5: 2 diet could be considered as a “lifestyle intervention,” fasting on alternate days (alternate-day fasting or ADF) is used more, usually, to lose weight quickly. Fasting on alternate days is also known as the "next day diet" and requires that the days be alternated between an unrestricted diet and the consumption of very few calories.

Most studies on fasting on alternate days use a criterion similar to the 5: 2 diet, which allows you to consume a small meal (usually about 500 kilocalories) on the days of "fasting."

Research has shown that fasting on alternate days can achieve significant weight loss over a period of 8 to 12 weeks. However, this fast poses a serious problem, and that is that diet monitoring usually declines. Long-term studies have shown that, over time, calorie intake is increased on "fasting" days, which reduces the caloric deficit achieved and slows the rate of weight loss.

Randomized controlled trials (the benchmark of clinical studies) have been carried out that show that fasting on alternate days does not achieve greater weight loss or more health improvements than traditional diets when calorie intake is the Same in both groups. However, fasting on alternate days usually results in a greater reduction in calorie intake than the traditional dietary method, which should result in greater weight loss in the initial phase. But it is unlikely that there are many people willing to practice fasting on alternate long-term days.

Restricted time feeding

The feeding in restricted time (time-restricted eating or TRE) consists of fasting completely for prolonged periods (from 16 to 20 hours) and consuming all the calories restricted periods, which are usually called “feeding windows”.

The most common variant of restricted time feeding uses a ratio between fasting and feeding 16: 8 (16 hours of fasting and 8 hours of feeding). Many people complete this cycle by skipping breakfast, so that they delay their first daily meal until noon and consume all food between noon and eight in the afternoon.

As some studies have shown, calorie intake in a 24-hour period is reduced when people skip breakfast. But the amount of calories spent by physical activity also decreases, which will totally or partially compensate for the caloric deficit achieved by skipping breakfast. Thus, skipping breakfast will not usually result in significant weight loss. Skipping breakfast also reduces the effectiveness of insulin to regulate blood glucose levels after food, indicating a negative effect on insulin sensitivity.

But there is an alternative method to restricted time feeding that has shown promising results. A recent study concluded that fasting after two in the afternoon improved insulin sensitivity in a group of prediabetic men. This result could be due to a greater natural ability to effectively regulate blood glucose levels in the morning, due to daily variations in metabolism. Thus, limiting food intake to a feeding window in the morning and fasting in the afternoon can be a healthier variant of the restricted time feeding method.

And the winner is…

As with all diets, success will be determined primarily by monitoring. When what is sought is to lose weight, fasting on alternate days is probably the one that will achieve the most immediate results, but to lose weight in a sustained way in the long term, the 5: 2 method, which is less helpful, may be more helpful. intense.

It has been observed that the follow-up could be greater in the restricted time feeding method, since some people may find it easier to completely limit food intake than to severely restrict it. In this sense, some studies suggest that skipping dinner may be more beneficial to health than skipping breakfast.

It is important to note that most studies suggest that intermittent fasting is not more effective than traditional dietary methods. But intermittent fasting regimes that contemplate prolonged fasting periods, such as the restricted time feeding method with shorter feeding windows and the 5: 2 diet with two consecutive days of intake of very few calories, can provide added benefits for health.

David Clayton, Lecturer in Nutrition and Exercise Physiology, Nottingham Trent University

This article was originally published in The Conversation. Read the original.

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