Skip Navigation

Expert Advice

Are There Any Proven Benefits to Fasting?

By Joe Sugarman
Mark Mattson is a professor of neuroscience in the Johns Hopkins School of Medicine and also serves as chief of the Laboratory of Neurosciences at the National Institute on Aging.

You probably know that too many calories aren’t good for your waistline, but as it turns out, they aren’t good for your brain either.

According to research conducted by neuroscientist Mark Mattson and others, cutting your energy intake by fasting several days a week might help your brain ward off neurodegenerative diseases like Alzheimer’s and Parkinson’s while at the same time improving memory and mood.

Mattson’s studies have built on decades-old research establishing a connection between caloric intake and brain function. In laboratory experiments, Mattson and his colleagues have found that intermittent fasting—limiting caloric intake at least two days a week—can help improve neural connections in the hippocampus while protecting neurons against the accumulation of amyloid plaques, a protein prevalent in people with Alzheimer’s disease. “Fasting is a challenge to your brain, and we think that your brain reacts by activating adaptive stress responses that help it cope with disease,” says Mattson. “From an evolutionary perspective, it makes sense your brain should be functioning well when you haven’t been able to obtain food for a while.”

But why fasting? Wouldn’t just eating fewer potato chips a day have the same effect? Apparently not, says Mattson. He explains that every time you eat, glucose is stored in your liver as glycogen, which takes about 10 to 12 hours to be depleted. After the glycogen is used up, your body starts burning fats, which are converted to ketone bodies, acidic chemicals used by neurons as energy. Ketones promote positive changes in the structure of synapses important for learning, memory, and overall brain health. But if you eat three meals a day with snacks between, your body doesn’t have the chance to deplete the glycogen stores in your liver, and the ketones aren’t produced. Mattson says exercise can also get your body to lower its glycogen levels, and not coincidentally, exercise has been shown to have the same positive effects on brain health as fasting.

Mattson recommends people try one of two strategies for incorporating calorie restriction. The first is called the 5:2 diet, which has gained popularity in recent years, particularly in England after the BBC aired a 2012 documentary called Eat Fast and Live Longer in which Mattson was featured. That diet calls for limiting your caloric intake to 500 calories two nonconsecutive days per week while eating a healthy diet in the normal caloric range (2,000 for women; 2,500 for men) the rest of the week. Five hundred calories

Fasting is a challenge to your brain, and we think that your brain reacts by activating adaptive stress responses that help it cope with disease.

means maybe a fried egg for breakfast and a small serving of lean protein with vegetables for lunch or dinner.

Another strategy is a time-restricted diet in which you pack all your meals into one eight-hour period a day so your body has time to exhaust its supply of glycogen, start burning fat, and produce ketones. Mattson says animal studies have shown that the time-restricted diet has effects similar to those of intermittent fasting.

If you do decide to try fasting, don’t dive in too quickly, Mattson advises. “The analogy with exercise applies here as well. If you’ve been sedentary and then all of a sudden you try to run five miles, it’s not very pleasant and you’ll likely get discouraged. It’s the same thing as if you’ve been eating three meals a day plus snacks, and then you’re not eating anything at all for two days; you’re not going to like it.”

Mattson suggests easing into the routine by starting with one day of moderate fasting per week and then building up to two. There will likely be a week or two of headaches, lightheadedness, and/or grouchiness, which are common side effects, but after the initial phase, experiments show that your mood should pick up.

Mattson collaborated on one six-month study of people practicing the 5:2 diet that demonstrated people’s well-being improved over time. Neurochemically, he says, when the brain is challenged by physical exertion, cognitive tasks, or caloric restriction, the body produces a protein called BDNF (brain-derived neurotrophic factor), which not only strengthens neural connections and increases the production of new neurons but can also have an anti-depressive effect. In his experiments with mice, he’s found that those with exercise wheels in their cages have higher levels of BDNF and show fewer signs of depression. “Probably during evolution, BDNF evolved to play an important role in increasing neuroplasticity in the brain and forming new synapses crucial to learning and memory as well as mood and motivation.”

But like so many others, will the 5:2 diet and its ilk become just another diet du jour?

“I hope it’s not a fad,” says Mattson, who is currently working on a study involving obese subjects at risk for cognitive impairment and the effects of intermittent fasting. “There’s a lot of science behind it, and the science is only increasing.”  /

Seven plates, five with food and two without, to signify two days of fasting a week.
Alex Robbins

Cutting your energy intake by fasting several days a week might help your brain ward off neurodegenerative diseases like Alzheimer’s and Parkinson’s while at the same time improving memory and mood.

Other Departments

  • Survey
    New findings in health, including the ill effects of interrupted sleep, the facts about cooking oils, and the genetics of nicotine addiction.
  • Ten Things
    10 Items to Safeguard Your Home
  • Just Curious
    What do surgical masks really protect against?
  • Book Report
    What you should be reading.
  • MedTech
    Apps, gadgets, and other innovations that are advancing health and health science.
  • Experience
    After bariatric surgery, Jessica Sharkey loses weight (and runs marathons).
  • Breakthroughs
    News from the cutting edge of research: A headband to treat Parkinson's, a device to help with vaccinations, and insights into dementia.
  • Conversation
    Jill Andrews, a graduate of New York’s Fashion Institute of Technology, made her first wedding gown in 1990. Now the wedding dress designer has used her couture skills to help design a better Ebola suit.