Multi-day fasting isn't worth downsides like hunger and loss of muscle mass, according to a nutritionist
- Fasting, or restricting food intake to specific days or time periods, has gained popularity in recent years as some research shows it can have benefits for weight loss, digestion, and even a longer life.
- Some forms of extreme fasting severely restrict calories, limit protein, or extend fasts for multiple days, potentially causing serious side effects.
- Nutritionist Robb Wolf argued in a recent presentation that the downsides of extreme fasting outweigh the benefits, and you can improve your health more easily by exercising and getting sunshine instead.
In the nutrition world, fasting has quickly become a buzzword, with multiple variations of calorie and time-restricted eating used by enthusiasts to help with weight loss, digestion, and even, potentially, slowing down aging.
While there's mixed evidence about fasting's benefits, the downside is obvious — too much of it can leave you hungry, low-energy, and losing hard-earned muscle mass.
That led nutritionist Robb Wolf, author of "The Paleo Solution" and "Wired to Eat", to wonder if there's a way to get the lifespan-extending benefits of fasting without the potential pitfalls.
"Once we hit something that looks like ancestral eating, getting adequate protein, right carb level, not overeating, I'm not convinced there's any upside to any calories restriction, protein avoidance, or fasting," Wolf said during the 2020 virtual KetoCon series of talks.
Some fasting practices, like time-restricted feeding or intermittent fasting, have proven benefits. But more extreme forms of fasting, which severely restrict calories or macronutrients like protein, or that extend into multi-day fasts, can have serious side effects.
'Calorie restriction is nothing more than defense against a terrible diet'
According to Wolf, one of the primary benefits of fasting for many people it simplifies their diet decisions. Not-eating naturally eliminates the most common eating-related problems, such as eating too much sugar, processed food, or just too many calories overall.
It's possible to avoid these dietary mishaps while still eating plenty of food, if you have an idea of what, and how much, to eat for optimal health.
That's easier said than done, especially in a world where calorie-dense, nutrient-poor processed food is flavorful and widely available, Wolf said.
But, he added, if you accomplish the "nontrivial" task of eating mostly whole, nutritious foods in moderation, you're likely to already get many of the benefits fasting provides by cutting out illness and aging-related compounds in unhealthy foods.
"If we're not eating a terrible diet, the benefits of calorie restriction appear to evaporate," Wolf said, citing a research paper on fasting and longevity in different species. "What this paper from biogerontology really suggests is that calorie restriction is nothing more than defense against a terrible diet."
Extreme forms of calorie restriction can have side effects such as lethargy, hunger, and loss of muscle
There is some evidence that fasting could also have benefits beyond what you don't eat, though. Researchers have suggested that fasting, or a severely calorie-restricted "fasting mimicking diet" can help slow aging and prevent chronic disease. That's in part because limiting food consumption, in particular keeping protein intake to a minimum, can help mediate how hormones are released in the body, slowing the aging process.
But Wolf says it's important to think about not just quantity but also quality of life. Fasting could potentially add years to your life (and in fact seems to do so in species like mice), research suggests.
To get the most out of fasting, you'd have to eat 40% less starting from childhood, at the cost of persistent hunger and fatigue, as well as a possible loss of sex drive and fertility (hypogonadism, linked to severe calorie restriction) and loss of muscle mass (sarcopenia).
Other strategies like exercise can improve lifespan without rigorous food restriction
Wolf said there are simpler solutions to living a better, longer life.
"We have some things that I think are well established but not particularly sexy when it comes to improving longevity," Wolf said. "There are some things that work maybe as well or better than calorie restriction and I would argue that they suck a lot less."
There's a wealth of evidence that regular exercise is one of the most important things we can do for health, with research linking physical activity to lower risk of cancer, a healthier heart, and even improved mental health.
Similarly, research has shown that simply getting enough vitamin D, which your body naturally produces when exposed to sunlight, can help lower the risks of dying.
Even coffee is associated with a better and longer life, with studies showing the beverage can lower risk of common ailments like diabetes, cancer, cardiovascular disease, and Alzheimer's.
Instead of fasting, consider just eating in moderation and practice other healthy habits, according to Wolf.
"You maybe lift weights 2 days, 3 days a week, do a little bit of cardio or running around, you get some or all of the potential benefits you would ever get from overt calorie restrictions," he said.
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