Intermittent fasting has been popular for several years now. While some attribute a multitude of health benefits to it and even see it as a miracle method for prolonging life, others remain skeptical of the many claims surrounding it. Benoit Arsenault, a researcher and professor at the Department of Medicine at the Université Laval, offers us a nuanced perspective on the issue, bridging the gap between science and social issues.
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Hello, Benoit. How would you define intermittent fasting? Why has it become so popular?
“Intermittent fasting is a dietary practice that alternates between periods of fasting and periods of food intake. Unlike other diets, it doesn’t dictate what you have to eat, but when you can eat. The most common approaches include limited eating windows, such as 16:8 (fast for 16 hours and eat for 8 hours) or 5:2 (eat normally for 5 days and significantly reduce calories for 2 days per week). This apparent simplicity, combined with tantalizing promises of weight loss and health benefits, explains its popularity. Many see it as an “easy” solution for consuming fewer calories without sacrificing their favourite foods in order to lose weight. Others do it for its alleged benefits on increasing life expectancy. But this approach raises many questions as to its actual effectiveness and long-term impacts.”
What are the main scientific findings on intermittent fasting so far?
“Over the past five years, many studies have explored the effects of intermittent fasting on human health. These findings have been consolidated into meta-analyses that give us a pretty clear picture. Let’s face it: the main reason people try intermittent fasting is weight loss. However, intermittent fasting results in modest weight loss: an average of one kilogram. In addition, this loss is often more attributed to a reduction in lean mass (muscle mass, bone mass, and water loss) than to a significant loss of fat mass. Certain short-term benefits have been observed on metabolic health, such as improved insulin and blood cholesterol levels and reduced inflammation, but these effects generally do not exceed those obtained through simple continuous caloric restriction. Intermittent fasting can be an attractive option for some people, especially those with metabolic health issues such as prediabetes, but it should be integrated into a holistic and sustainable health approach.”
Could intermittent fasting really extend your lifespan?
“It’s a fascinating question, but the answer is still far from being settled. In insects such as fruit flies and some animal models, studies have shown that intermittent fasting could extend their lifespan. However, these results vary according to the species and the experimental conditions, and some negative consequences, particularly on the immune system, have been observed. For example, laboratory mice, which live in highly controlled environments, might benefit. On the other hand, wild mice, living in more realistic conditions, don’t achieve the same results. This illustrates that the effects of intermittent fasting are highly dependent on context. In humans, we lack long-term data. We know that intermittent fasting can reduce certain blood biomarkers associated with aging, but it’s difficult to say whether these changes translate into a real increase in life expectancy and whether the benefits of this practice outweigh the consequences.”
What are the risks or limits of intermittent fasting?
“Intermittent fasting is not without risk, and its reckless application can have negative consequences. Motivated by influencers or ‘coaches’ on social media, some people adopt overly strict or prolonged forms of fasting without supervision. This can lead to nutritional deficiencies, fatigue, digestive issues, and even excessive loss of muscle mass. The promises of exceptional benefits for health and longevity are not supported by solid evidence, which can lead to disappointment or rapid abandonment. Intermittent fasting can also exacerbate eating disorders, particularly in young women. Cycles of fasting and overeating can harm our relationship with food and affect self-esteem. If I had one piece of advice to give to people who are contemplating intermittent fasting, it would first be that they should be aware that it requires a significant long-term commitment, but also that they should work as a team with a nutritionist belonging to the Ordre des diététistes-nutritionnistes du Québec in order to ensure that this process is undertaken safely and that realistic goals are set.”
What do you think of the commercialization of intermittent fasting?
“It’s a subject that’s both fascinating and worrying. I didn’t think it was possible to profit from this practice, but it’s clear that fasting has become a lucrative market. Apps, programs, supplements, and even ‘fasting kits’ claim to optimize this practice, obviously without solid scientific evidence. Celebrities and social media influencers promote these products, sometimes with exaggerated claims lacking nuance. These products are expensive and useless.”
Is the practice of intermittent fasting compatible with an active lifestyle?
“In some cases, intermittent fasting may be compatible with an active lifestyle, but it depends on several factors, particularly individual needs, the type of activity practiced, and the approach adopted. The main consideration is that physical activity requires a sufficient energy supply to optimize performance, promote recovery, and prevent injury. In practice, intermittent fasting can pose challenges for active people, especially if the eating windows don’t correspond to the times of high energy needs, such as before or after a workout. Furthermore, an insufficient caloric intake can lead to a loss of muscle mass, decreased energy, and increased fatigue, thereby compromising the ability to maintain an active lifestyle. For active people, a balanced diet spread out properly throughout the day often remains a more suitable option for supporting their health and performance goals while promoting a healthy relationship with food.”
In your opinion, what is the best approach to promote health and longevity?
“The science is clear: there’s no miracle solution. To promote health and wellness, we should focus on fundamental principles such as a balanced diet. Cooking and eating a variety of quality foods, not excluding any food groups, putting colour on our plates, sharing meals with family or friends, and paying attention to our hunger and fullness signals are among the key elements of a diet compatible with life expectancy in physical and psychological health! Two other factors which are often neglected—stress management and sleep—should also be considered. Regular physical activity, however, remains THE main determinant of healthy life expectancy.”
Access the social networks, YouTube channel, and Les voies métaboliques podcast hosted by Professor Arsenault.
