Obesity has a multifactorial and complex etiology. Genetic, metabolic, psychological, social and environmental factors interact. It is a major public health problem worldwide, and its frequency is increasing in children and adults in both developed and developing countries.
The majority of people with obesity who manage to lose weight through any method regain it after 2 years of follow-up. It has been shown that if healthy changes in eating and lifestyle habits are not maintained over the long term, the weight will be regained sooner or later.
Obesity is therefore a disease that is a growing, complex and frustrating problem, both for patients and for the nutritionists who treat them.
Intermittent Fasting is all the rage but is it safe and effective?
Intermittent fasting (IF) or intermittent calorie restriction is a relatively new approach to overweight and obesity that has attracted the attention of researchers and has become popular with the general public in recent years. However, despite its growing popularity, scientific evidence on the safety and effectiveness of this method in relation to other dietary approaches is still very limited.
There are several hypotheses about its mechanism of action: resetting of the internal circadian clock and induction of catabolic circadian rhythms, stimulation of the cellular stress response, hormonal changes, etc.
Preclinical studies show that IA increases the adaptive response to stress, increases the elimination of damaged proteins from the body, increases the mobilization of body fat, beneficially modulates the intestinal microbiota, decreases cell proliferation, improves insulin sensitivity and decreases systemic inflammation. In addition, animal studies (mice) show that IA can help to lose weight regardless of calorie intake, improve body composition (maintain muscle mass and lose fat), and protect against chronic diseases such as diabetes, cardiovascular disease, cancer and neurodegenerative diseases (Alzheimer’s disease). It appears that these positive effects on metabolism and disease risk are partially independent of weight loss.
However, there is little scientific evidence in humans on the independent effects of UA on weight loss. Two clinical trials in women have been published showing that AI improves insulin sensitivity despite losing the same weight as continuous calorie restriction -CCR- at 4-6 months of treatment. One of these two studies also showed greater fat mass loss on AI. In a clinical trial of 6 months of intervention with AI and 6 months of maintenance, no differences in weight loss were observed between individuals following an AI with respect to those following a continuous CCR diet. Nor were differences in metabolic and cardiovascular risk factors observed. Instead, a higher number of dropouts were observed in the AI diet, i.e., lower adherence (Trepanowski et al, JAMA 2017). Another 2-year clinical trial published in 2017 (Aksungar et al, J Nutr Health Aging), but which was conducted in a very small sample of women (n=23) following AI (15h fasting per day, but without total caloric restriction) showed improvement in blood levels of glucose, insulin and insulin resistance.
There are no medium- or long-term studies on the effect of UA on adherence (ability to follow treatment and not drop out). It is still unknown – there is no scientific evidence – whether UA is effective in real-life situations.
The only human clinical trial that can provide reliable data on adherence, weight loss, metabolic markers (glucose, cholesterol, etc.), body composition, gene expression and psychosocial factors is ongoing, but its results have not yet been published. It is the HELENA study, initiated in 2016, a trial on 150 adult subjects who are followed for 2 years to evaluate the AI 5:2 (5 days off and 2 days of caloric restriction).
Caloric restriction or fasting is known to increase longevity in animals and prevent diseases such as cancer, diabetes and cataracts. It is postulated that AI could be useful in the face of chronic caloric restriction, preventing the adverse effects of chronic caloric restriction, such as malnutrition.
In practice, despite the theoretical or possible benefits of AI, its effectiveness may be limited by the difficulty of being followed in real life, either by hunger during periods of fasting, compulsive or compensatory intake during periods of non-caloric restriction, possible fatigue or decreased energy, or the possibility of headaches or headaches in susceptible individuals.
Intermittent fasting, a promising alternative for weight loss but little contrasted
In short, IF is postulated as a promising modality of dietary pattern for the treatment of overweight and obesity and its metabolic complications, although more scientific evidence is still needed to confirm or not its superiority over other types of diets. On the other hand, there are no studies that show possible differences in the effectiveness of the different IA modalities.
AI should not be followed in the following cases:
- Type 1 insulin-dependent diabetes
- Pregnancy
- Breastfeeding
- Eating behavior disorders
- Hepatic or renal insufficiency
- Intake of certain weight loss medications, such as metformin and Victoza
AI is a dietary guideline option for adults who want to control their weight, patients who are overweight and obese or have cardiovascular risk factors, but it should be prescribed and followed individually by a medical nutritionist and supplemented appropriately if required.
It should not be forgotten that during periods of “non-fasting” a healthy diet should be followed, rich in plant foods, healthy fats (from olive oil, avocado, nuts, seeds or oily fish) and healthy proteins (from fish, eggs, white meat or whole grains, legumes and pseudocereals such as quinoa). It should also be low in foods with a high glycemic index (refined cereals, sugars, sugary foods and drinks) and in saturated fats (red meat, sausages, full-fat dairy products) and trans fats (present in processed and ultra-processed foods).
On the other hand, during the fasting period, do not forget to drink enough liquids (water, coffee, tea, herbal teas, broths). Finally, intense physical exercise is not recommended during the fasting period.
Of course, AI should be accompanied by other measures for weight control or weight loss such as regular physical exercise, the practice of stress and anxiety management skills and mindfulness eating techniques.