The intermittent fasting craze came in like a lion — and turns out, we got a few things wrong in the frenzy. In an endeavor to unpack the hype and separate fact from sensationalism, we sat down with Dr. Valter Longo, director of the University of Southern California’s Longevity Institute and author of “The Longevity Diet.”

Here’s his take on the intermittent fasting (IF) craze and some tips to help you understand the concept accurately and implement it more effectively.

1. Our terminology is wrong

For starters, intermittent fasting doesn’t mean what we think it does. When we talk about Leangains 16:8 protocol or the 5:2 diet as methods of intermittent fasting, the concept we’re really referring to is ‘time-restricted feeding’ (TRF).

In “The Longevity Diet,” Dr. Longo explains that the label intermittent fasting “represents a problematic direction because it allows people to improvise and pick and choose periods of fasting that range from 12 hours to weeks, giving the impression that… some ‘abstention from food’ is similar or equivalent, and all provide health benefits.”

Dr. Longo’s advice: To get in the right mindset, he recommends to “start using the right terminology.” It’s not fasting if you’re going without food for 24 hours or less — the correct term is time-restricted feeding.

2. Going extreme isn’t always better

Popular intermittent fasting advice online says to abstain for 16 to 24 hours between feeding periods on a regular basis. However, Dr. Longo advocates a feeding window of 12 hours per day for optimal health.

While clearly the diet psychology of IF appeals to some people, even done short term, conventional IF advice may come with health risks.

According to Dr. Longo, if you eat only for four to six hours a day, “then you start to see gallstone formation [and] increase the chance that you’re [going to] need your gallbladder removed.” Studies show that elongated periods between eating increases the risk of gallstone formation in women, regardless of weight.

While research hasn’t found the exact connection, studies indicate there’s a correlation with people who skip breakfast tending to have much higher rates of cancer, cardiovascular disease, and mortality.

Extreme limited feeding windows and alternate day fasting can also cause problems with cardiovascular disease, whereas 12-hour TRF was shown in a study on flies to decrease age-related cardiac decline.

On the other end of the spectrum, “If you eat 15 hours a day or more, that starts to be associated with metabolic problems, sleep disorders, etc.”

Dr. Longo’s advice: Eat for 12 hours, then refrain for the next 12. Stick as closely to this daily feeding schedule as possible to minimize adverse health effects.

3. Time-restricted feeding isn’t a quick fix — it’s a long-term lifestyle

It’s easy to buy into the hype of drastic dietary quick fixes, but you rarely hear of the person who lived to be 100 subsisting on a fad diet. Dr. Longo uses centenarian studies to serve as one of the five pillars supporting his longevity research because they often reveal what clinical studies can’t in terms of long-term effects and real-life practicality.

Dr. Longo suggests trimming down to two meals plus a snack — versus his usual recommendation of three meals and a couple of snacks per day.

Eating a pescatarian diet (no meat, except seafood), consuming low but sufficient proteins through age 65, and low added sugar intake are other key practices found in high-longevity zones.

Dr. Longo’s advice: We can learn a lot from our elders’ eating patterns, especially the oldest among us, as they’re living proof of what promotes health-span and lifespan.

Does intermittent fasting help you live longer?In one article, Scientific American dives into the data around IF and found that research suggests it could help with longevity, but the results aren’t conclusive.

4. The optimal feeding window doesn’t have to be hard to achieve

Dr. Longo’s recommended 12-hour daily feeding window? You might already be doing it. For example, if you eat breakfast at 8 a.m., lunch around noon, and cut your eating off after dinner by 8 p.m., forgoing a nightcap — you’re in the sweet spot. The main thing you’ll need to be vigilant about is late night snacking, something most of us are guilty of, at least occasionally.

Dr. Longo’s advice: Don’t eat anything within three to four hours of bedtime. Be vigilant but also simple: Confine all eating within a 12-hour period — for instance, if you start at 9 a.m., make sure you end by 9 p.m.

5. Restrict portion size, not feeding window, to lose weight

If you’re already restricting your meals to a 12-hour timeframe, how do you get the number on the scale to budge?

Dr. Longo suggests trimming down to two meals plus a snack — versus his usual recommendation of three meals and a couple of snacks per day. People who have issues with obesity or being overweight are more likely to overeat each time they eat, which is why limiting the number of meals and snacks is imperative for those striving to pare down.

Listen to your bodyIt’s also important to truly listen and know your body. Studies on mice suggest that if people feel restricted, overeating may occur. However, another study using mice also shows that fasting on the weekdays helps prevent weight gain. If TRF causes more anxiety and weight gain, then it’s not for you. There are many other eating plans to try, such as the Mediterranean or low-carb.

Different body types have different standards. This is what Dr. Longo recommends, based on his own research and practice:

  • For those trying to lose weight — men with a waist circumference above 40 inches, and women whose waists are 34 or more inches — it’s best to eat breakfast and either lunch or dinner, plus a nourishing, low-sugar snack.
  • Men with a waist circumference below 33 inches and women with a measurement of 27 inches or less should eat three meals and a couple of snacks per day.

Nutritious meal suggestions from Dr. Longo’s book include:

  • whole wheat focaccia with no sugar added blueberry jam for break
  • spinach with pine nuts and raisins for lunch
  • pasta with broccoli and black beans for dinner
  • a healthy snack like some nuts, carrots, or dark chocolate

Dr. Longo’s advice: Keeping portion size under control every time we eat is critical. Instead of counting calories, we should monitor food labels to ensure that we’re getting sufficient nutrients like protein, vitamins, minerals, and omega fatty acids.

6. Don’t skip breakfast

It’s common for intermittent fasters to wait until 1 p.m. to have their first meal, but Dr. Longo strongly advises against skipping breakfast. While research hasn’t found an exact connection, studies indicate that people who skip breakfast tend to have much higher rates of cancer, cardiovascular disease, and mortality.

They’re also more likely to have worse heart and overall health, as well. If you’re going to skip a meal, make it lunch or dinner, and definitely nix before bed snacking.

While Dr. Longo acknowledges that there are alternative explanations other than long fasting periods for why skipping breakfast is associated with increased mortality, he urges this link alone should represent a major warning and concern. According to Dr. Longo, there’s notably very little negative data associated with 12-hour TRF, which is also practiced by most long-lived populations around the globe.

Dr. Longo’s advice: Breakfast doesn’t have to be a big ordeal. If you typically wait until mid-day or later to eat because of time or convenience, it’s easy to incorporate a light breakfast of tea or coffee, plus toast with preserves, into your morning routine.

There’s no fast track to wellness

Time-restricted feeding isn’t a quick fix for perfect health, because there’s no fast track to wellness. For some people, this method of eating may not work for their lifestyle — if fasting causes you to binge or overeat on the weekends or cheat days, it may not be for you. (According to Harvard Health Publishing, 38 percent of those who tried fasting dropped out.)

If you’re considering time-restricted feeding, speak with your doctor first as skipping meals and limiting calorie intake isn’t recommended for people with certain conditions such as diabetes or those with a history of disordered eating.

Living life to the fullest is about making slow and steady tweaks to your habits. As with most healthy eating protocols, a quick fix isn’t the answer — building foundational support that’ll support your health in the long-run is.


Courtney Kocak is a writer on Amazon’s critics’ choice-nominated animated series Danger & Eggs. Her other bylines include the LA Times, Bustle, Greatist, and many others. Follow her on Twitter.