Your Guide to Intermittent Fasting

Your Guide to Intermittent Fasting

Find out what to eat and when for optimal results.

You may opt for one fad diet or another—Paleo, Keto, Alkaline (Tom Brady’s) or Carb Cycling—but none of them take into account an essential truth about your body: it uses calories, fat, carbs and glucose differently at different times of the day.

Studies show that eating the same amount of calories early or later in the day produces two very different results. Front load your food intake so you get 80 percent of your calories before 1 or 2pm and you can lose weight. Eat more than 20 percent of your calories in the evening and you’ll have trouble losing weight and may even pack it on. That’s because timing is everything—in music, love and nutrition.

Your body is made to consume food while the sun is shining—and to not consume food while it’s dark. That aligns with the healthy choice of having at least 12 hours between dinner and breakfast.

How to schedule your eating
One option that can help you cut out your late-night snacking or dinner-then-right-to-bed syndrome is to consider some kind of intermittent fasting schedule. You eat so there’s a chunk of hours in the day when you don’t consume anything but water, coffee or tea.

It can improve your nutrition, super-power your energy level, help you sleep, reduce your risk for type 2 diabetes and promote weight loss and improved HDL and LDL cholesterol levels. (That is, if you don’t overeat on non-fasting days.)

How does it do that? As Mark Mattson, the senior investigator for the National Institute on Aging says, “There is considerable similarity between how cells respond to the stress of exercise and how cells respond to intermittent fasting.” True, most studies have been done on lab animals, but there’s mounting evidence that intermittent fasting is beneficial.

  • One study of overweight adults with asthma had participants eat just 20 percent of their regular caloric intake on alternate days for eight weeks. The results: They lost 8 percent of their initial body weight, reduced levels of markers of oxidative stress and inflammation and saw asthma symptoms and quality of life improve.
  • Multiple studies indicate that intermittent fasting may help stimulate production of adult stem cells, particularly in the intestines and skeletal muscles, which are essential to counter the decline in bodily functions associated with aging.

So what are your choices?
In What to Eat When, Dr. Mike’s new book with Dr. Michael Crupain (out December 31st), the “When Way guidelines” are:

  1. Fast each night with at least 12 hours between dinner and breakfast. Want more benefits? Extend that to 14 hours and then 18. This causes your body to burn up most circulating glucose and stabilizes insulin levels. Then your body burns stored fat.
  2. Breakfast and/or lunch should contain lean and plant-based protein (think whole grains, legumes, salmon) and fats (think healthy fats in salmon or use EVOO with grains and veggies). Because your body is naturally more insulin-resistant at night, avoid simple carbs after midday. Dinner should be plant-heavy (salad and other green, leafy veggies) and calorie-light (about 400 calories, if you need 2,000 a day to maintain a healthy weight).
  3. The Longevity Institute at USC says you can super-power your health and boost weight loss by reducing your calorie intake to 1,000 for one day, 750 for four days. Then resume eating the When Way.  

Other patterns for intermittent fasting
You may want to try eating for eight hours—say noon to 8pm daily—and fasting for 16. Or try the two-five routine, in which you restrict your intake to 500 calories a day twice a week. Then, five days you eat a healthy, full complement of calories (1,800 to 2,400 for most folks). And then there’s the Warrior plan—eating during four hours a day and fasting for the remaining 20. Check out to see one amazing guy who loves this! Also, to help you stay on track, take note of your food intake on the Sharecare app for iOS and Android.

Medically reviewed in November 2019.