Dr Martin Juneau, M.D., FRCP

Cardiologue, directeur de l'Observatoire de la prévention de l'Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention Watch, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.

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12 July 2017
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Intermittent fasting: A new approach to weight loss?

The excessive accumulation of body fat, particularly when concentrated in the abdomen, is an important risk factor for several diseases, including heart diseasetype 2 diabetesdementia as well as several types of cancer. Consequently, for people who are overweight or obese, weight loss is a very important way to reduce the incidence and progression of several of these diseases.

Many studies show that weight loss is indeed associated with a significant improvement of several aspects of the metabolism. For example, an American study showed that among overweight individuals with diabetes, a 5-10% loss of body weight was associated with a notable improvement of several risk factors for heart disease (glycemia, blood pressure, triglycerides, HDL cholesterol) after one year.  These positive effects are even more pronounced when weight loss is more significant, in particular with regard to sugar metabolism, but the key takeaway is that weight loss, even when relatively modest, has a very positive impact on health.

Unfortunately, losing weight is not a “small” matter, since it entails significantly reducing calorie intake for long periods.  However, the results of the CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) study show that it is possible: in this study, conducted over two years, participants successfully reduced their calorie intake by 12%, which translated into a 10% weight loss and a significant improvement of several cardiometabolic risk factors. However, this decrease in calorie intake was well below what researchers wanted (25%), even though participants were closely monitored and could ask for advice from several specialists in the research team.  Significantly reducing food consumption, namely by 500 to 600 calories daily, thus represents a difficult objective to achieve for most people, which explains the well-documented difficulty of adhering, in the long term, to popular weight loss diets developed over the last few years.  Generally, these diets are associated with relatively significant short-term weight loss, but it is very difficult to maintain this loss in the longer term and the majority of people regain the lost pounds (and sometimes even more) after a certain time.  When these diets are repeatedly attempted, they cause what is known as the “yo-yo” effect, which is not only discouraging but can also be harmful to health: in fact, a recent study showed that in patients with a history of cardiovascular events, frequent body-weight fluctuations were associated with a marked increase in the risk of myocardial infarction (117%), stroke (136%), diabetes (78%), and premature death (124%).

Strict but brief restriction
To overcome these limitations, more and more researchers have focused on fasting as a way to take advantage of the benefits associated with caloric restriction.  Instead of consistently reducing the number of calories consumed every day, which seems virtually impossible for the majority of people, this approach involves alternating periods of normal calorie intake with more or less prolonged fasting periods. What we refer to as “intermittent fasting”, for example, consists of fasting or drastically reducing calorie intake (500 calories a day) intermittently, for example, 1 or 2 days a week. These fasting periods can be consecutive, as in the 5:2 diet (5 days of normal diet followed by two days of fasting), or alternating (one out of two days, for example). In both cases, studies show that intermittent fasting is associated with weight loss and an improvement of several cardiometabolic markers, similar to the results obtained following continuous caloric restriction, and could therefore present an interesting alternative.

Nevertheless, an inherent limit to this type of strict fasting is that it remains very difficult for many people to completely deprive themselves of food for 2-3 days. Not to mention that the complete elimination of calories can lead to severe complications in some people, in particular in elderly or frail subjects.

It is in this context that Dr. Valter Longo’s team (University of South California) came up with the idea of developing a diet that reproduces the positive effects of fasting on the body, but without completely forgoing food. Their research conducted on mice showed that a less strict caloric restriction (calories reduced by half), achieved through a plant-based diet high in polyunsaturated fats but low in protein and carbohydrates, could mimic the effects of very strict fasting on several cardiometabolic risk factors and was associated with a significant improvement on health (fewer cancers, reduction in bone-density loss, improvement of cognitive performance) as well as of the life expectancy of the animals. Referred to as the “fasting mimicking diet” (FMD), this new type of caloric restriction could thus represent a new approach to not only lose weight but also improve health in general.

This strategy’s potential is clearly illustrated by the results of a phase 2 clinical study recently published in Science Translational Medicine. The 100 study participants were divided into a control group that followed their usual diet, and a study group that were prescribed the FMD for 5 consecutive days every month, for a period of three months. Afterward, the groups were switched, meaning that the participants from the first control group tested the FMD, whereas the volunteers in the study group reverted to their usually dietary habits.

The results obtained are extremely interesting.  One week following the end of the third caloric restriction cycle using the FMD, participants had lost on average 3 kilos (6.6 lb.), had a smaller waistline (3 cm), and showed an improvement in their blood pressure compared to the control group (- 4 mm Hg). Positive effects of caloric restriction on fasting glucose, the lipid profile (triglycerides, cholesterol), inflammatory protein levels (C-reactive protein), and certain growth factors such as IGF-1 (implicated in the development of cancer) were also observed, in particular in individuals who presented anomalies in these markers at the start of the study. For example, the blood sugar level of participants who were prediabetic at the beginning of the study returned to normal after the intervention.

Caloric restriction using the FMD is still at the experimental stage and further research is necessary to better evaluate its effects in the longer term. In the meantime, one thing is certain: most chronic diseases currently affecting the population are a consequence of the overconsumption of food, and there are only advantages to eating less, even if only a few days a month.

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