Is intermittent fasting the best way to eat for our weight and health?

Intermittent fasting has been the subject of a lot of research and intense conversation of late. A recent review article in The New England Journal of Medicine adds fuel to the debate. What are the pro’s and con’s of intermittent fasting? Is it the easiest way to lose weight? Is it the best strategy for health and longevity? I don’t know if we totally have the answers to these questions just yet, but some conclusions can be drawn from the data we have so far.

The Article 

The article was published in late December in The New England Journal of Medicine by two researchers from John’s Hopkins University School of Medicine (Reference 1). The main thrust of the article is to present the health benefits of intermittent fasting. The authors argue that fasting turns on adaptive cellular responses that improve glucose regulation, increases stress resistance and suppresses inflammation. 

The article discusses the three most studied fasting protocols:

-Alternate day fasting.

-5:2 intermittent fasting, where you fast for 2 days each week.

-Daily time restricted feeding.

The article goes on to describe research that found benefits of intermittent fasting on aging and a wide variety of disease processes, including: cognitive function, obesity, diabetes, cardiovascular disease and cancer.

Conclusions And Recommendations

1) This article presents some very interesting research concerning the health effects of intermittent fasting. This is a well written and well researched article published in the top medical journal in the world. The researchers make some compelling arguments about how fasting can improve health. I think the research in this area is in a really early stage and we need to do a lot more before we have any definitive answers.

2) Having said that, most of the research has been on animals. This can be a problem because animals have a very different physiology compared to humans and many times animal research does not translate to humans much at all. The authors mention this in the conclusion: “Animal models show that intermittent fasting improves health throughout the life span, whereas clinical studies have mainly involved relatively short-term interventions, over a period of months. It remains to be determined whether people can maintain intermittent fasting for years and potentially accrue the benefits seen in animal models” (Reference 1).

3) When it comes to weight loss strategies, I am not at all convinced that intermittent fasting is the way to go. I feel this way for several reasons:

-In most of the studies that I have seen, there is no greater weight loss when comparing fasting and a more standard continuous calories restriction. I researched two of the weight loss studies cited in this review (References 2 and 3). These studies compared continuous calorie restriction to intermittent fasting. In both of these investigations, the amount of weight loss was the same whether fasting was used or continuous calorie restriction was used as a method of weight loss. 

-While there were some benefits to those who fasted, including improved fasting insulin and insulin resistance, there were some negatives as well. Several other research investigations that I have covered in my blog showed negative outcomes with diets using intermittent fasting. These include: an increased LDL cholesterol, glucose dysregulation, increased inflammation, increased hunger, a decreased physical activity level and a decreased energy expenditure. If you want to reference these studies, please refer to this older blog post (click here).

-There can be some real side effects to intermittent fasting. This was apparent in both of the weight loss studies that I downloaded from the review. In the British Journal of Nutrition article, subjects in the intermittent fasting group were more likely to report constipation, headache, feeling light-headed and being preoccupied with food as side effects (Reference 2). Furthermore, the subjects fasting were more likely to have deficiencies in important nutrients such as magnesium, zinc, selenium and fiber.
In the International Journal of Obesity article, subjects fasting were more likely to report negative side effects such as lack of energy, headache, constipation, lack of concentration and hunger (Reference 3).

-Another major issue for me is the nutritional composition of the diet. If you are seriously restricting your food intake several days each week, there is no way that you will be getting enough vitamins, minerals, fiber, antioxidants, fruits, vegetables, etc. Supplementing with vitamins is just not the same.

In conclusion, this article on fasting in The New England Journal of Medicine is very interesting.  There appears to be some real health benefits for animals. It remains to be seen if these benefits translate to humans over the long term. As a weight loss strategy, it is my opinion that fasting is not the easiest or most effective strategy.

References

1) de Cabo R, et al. Effects of intermittent fasting on health, aging and disease. New England Journal of Medicine 2019; 381:2541-51.

2) Harvie M, et al. The effect of intermittent energy and carbohydrate restriction v daily energy restriction on weight loss and metabolic disease risk markers in overweight women. British Journal of Nutrition 2013; 110:1534-47.

3) Harvie M, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity 2011; 35:714-27.