There are several types of fasting. However, there are few studies that support the results on our health in the medium term and the scientific community has many doubts about the effect that this practice has on health.
The different types of fasting are
- Physiological fasting: not eating overnight (8-12 hours).
- Daily intermittent fasting: at least 12 hours of fasting.
- Weekly intermittent fasting: fasting one/two days a week.
What does intermittent fasting do to our body?
Glucose and fatty acids are the main sources of energy for the cells. After meals, glucose is used as an energy source and fat is stored in adipose tissue as triglycerides.
During periods of fasting, triglycerides are broken down into fatty acids and glycerol and are then used for energy. The liver converts fatty acids into ketone bodies, which provide a major source of energy for many tissues, especially the brain, during fasting. Ketone bodies are not only fuel for fasting periods, but are potent molecules that signal important effects on cells, and on the functions of our organs. Thus, ketone bodies regulate the activity of many proteins and molecules that influence health and aging.
It is this fundamental substrate change (the use of ketone bodies instead of glucose) that seems to be the explanation for the possible benefits of fasting.
Is intermittent fasting advisable if you want to lose weight?
Intermittent fasting may have beneficial effects in relation to diabetes and obesity, but more scientific studies are still needed to prove it. Some scientific articles evidence benefits of intermittent fasting. However, many also cautiously point out the interpretation of their results and the need to broaden the study conditions to issue statements that explain the full functionality of intermittent fasting and its relationship with cortisol in humans.
This is important because it is known that, when fasting, there is a great loss of energy that the body requires, and it is here where cortisol participates, regulating the metabolism and the immune system, which would cause various scenarios, both beneficial and adverse, affecting the health of the person.
After analyzing various studies, the scientific evidence shows that fasting has beneficial effects on weight loss and on the improvement of cardiometabolic variables, but these effects are not superior to those obtained with the traditional method of daily calorie restriction.
Pros and cons of intermittent fasting
Intermittent fasting is a practice that, despite still having little scientific basis, generates a number of pros and cons:
- Pros of intermittent fasting: The main use currently attributed to it is in relation to the loss of adipose tissue, where it seems to have good results. Although it seems to be an efficient alternative in weight loss, the ability to maintain the lost weight without regaining it in the long term will have to be evaluated with additional studies.
- Cons of intermittent fasting: Any restriction has a psychological component associated with it and also a level of adherence that, in most cases, if too demanding, leads to failure. Recent studies confirm a relatively high dropout rate when this type of program is initiated. In addition, symptoms are associated with: feelings of hunger, dizziness, headaches, difficulty in maintaining concentration, altered absorption of medications, nutrient deficiencies and even eating disorders.
Why has intermittent fasting become so fashionable?
Nowadays there are many actresses and instagrammers promoting intermittent fasting and people are copying it.
“Stopping eating” does not educate to learn how to maintain a healthy, balanced diet. Some people are not affected by going periods without eating and, without eating disorders, fasting can work for them.
However, the recommendation of doctors specializing in Nutrition and Dietetics, is that it is healthier and more sustainable to bet on a balanced nutrition and a change of habits to bet on health.
- Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutrition and Healthy Aging 2018 (4): 345-353
- Effects of time-restricted feeding on body weight and metabolism. A systematic review and meta-analysis. Reviews in Endocrine and Metabolic Disorders (2019) https://doi.org/10.1007/s11154-019-09524-w
- Effects of Intermittent Fasting on Health, Aging, and Disease. NEJM 2019; 381: 2541-2551