The New Rules of Intermittent Fasting and Time-Restricted Feeding


You need to understand what new scientific studies have discovered, especially the latest one from the University of Tennessee. (You may have seen it covered in the news.)


First, there’s the issue of exactly what is “intermittent fasting.”

Lots of health gurus seem to have “moved on,” leaving intermittent fasting behind. They’re promoting time-restricted feeding (TRF) as all you need. It doesn’t matter what you eat, just when you eat it. Or, so they claim.

Or they call time-restricted feeding intermittent fasting. The U of T study and its coverage in the popular press does exactly that too.

(They are related. They overlap, but they’re different.)

IF has generally meant going without food for a long enough period of time that it’s an actual fast – but a relatively short one. Nothing extreme, like 40 days in a desert.


That means not eating for one to three days. 

(Any fast longer than three days is serious, and should probably have medical supervision. Even three days may be risky for some people, depending on age and medical condition. If you’re not sure, ask your doctor.)

Myself, I started IFing with Brad Pilon’s book EAT STOP EAT. He recommends going without food from the end of one meal to the same meal the next day – 24 hours.


That is, today you eat dinner, but nothing after dinner. Tomorrow: no breakfast, lunch, or snacks. But you eat dinner tomorrow evening.

I prefer going from breakfast to breakfast. Pilon leaves it up to your choice. But, according to recent research, eating in the morning is the optimum choice. More on that in a moment.


Brad suggests doing that one or two days a week and eating normally the other five to six days. 

That helps you lose weight, reduces your blood glucose and insulin, lowers your blood pressure, and gives you the many other benefits of IF.

But now TMF is becoming more popular. 

And so the gurus need to start clarifying their advice in light of recent research.


What is Time-Restricted Feeding?

You set a specific “window” of eating time every day. Before and after, you refrain from eating.

Remember: Many Americans are pigging out 16+ hours every day. They eat right after they wake up, then have lunch and dinner, with snacks in between and snacks even after eating dinner. Some even wake up and eat in the middle of the night.

Small wonder high blood sugar and insulin are practically at epidemic levels. Type II diabetes is increasingly common.

For TRF, a 12-hour window is a minimum. If you eat breakfast after waking at 6:00 AM, you have until 6:00 PM to eat dinner.


Many people go for an 8-hour window.

Others are more extreme. They eat for only four hours a day – or even have just one meal per day.

But according to a just-released study from the University of Tennessee, one-meal-a-day folks are increasing their mortality risk by 30%. That’s a shocking conclusion.


It’s undoubtedly beneficial to give your digestive system a daily rest, especially during the four hours before you go to bed – digesting food interferes with your sleep cycles – and all through the night.

But trying to cram all your caloric and nutritional needs into one meal is itself stressful – probably causing huge spikes in blood sugar, which are not healthy.

And other recent studies now say a TRF window should not be during just any 8-hour or so time period.

They should be weighted toward eating in the morning, NOT the evening.


See, studies do show TRF is effective for reducing blood sugar, losing weight, and other such benefits – similar to intermittent fasting.

There’s just one small problem with many of those original studies: they were carried out on rodents.

Studies done on people are not nearly as conclusive on the health benefits of TRF for people.


Rodents Live a Lot Shorter Lives Than Human Beings

When scientists put rats on an 8/16 window of TRF, that’s NOT equivalent to you eating only from 12:00 noon to 8:00 PM every day.

One doctor has estimated that a rat going without food for 16 hours is roughly equivalent to a person fasting for 64 hours – about 2 1/2 days.

If you spent your entire life alternating eating only for 1 1/4 days, then fasting for 2 1/2 days, you’d be thinner too.


I’m not certain that is truly equivalent, because rats and mice also have biological clocks synced with the 24-hour movement of the sun.

But that’s probably a big part of why TRF doesn’t always work well in people – our bodies are also on a Circadian cycle.

Because we’re awake during the daytime, our bodies most want food during the day – especially in the morning. That’s supposed to supply us with the energy to spend our days hunting and gathering so we have food tomorrow.

Yet many people practicing TRF are skipping breakfast and getting most of their calories at dinner, or even later than 6:00 PM. That’s going against our natural, daily biological cycle.

Any reasonable – not extreme – TRF practice is certainly healthier than stuffing your face for 16+ hours, but you should consume most of your calories in the morning, not in the afternoon, and certainly not after 6:00 PM.

Also, many people doing TRF are skipping intermittent fasting, and that may limit their results.


Don’t Neglect True Intermittent Fasting

One or two 24-hour fasts per week, as Brad Pilon suggests, give your body time to carry out more extensive autophagy.

Autophagy is when your body repairs damaged cells, cleans up metabolic debris, and recycles those old proteins into new, healthy cells.

Autophagy requires low levels of insulin in your blood, so it doesn’t happen when you constantly eat.

It takes around 16 hours of not eating to ramp the process up. Eat – because your TRF eating “window” is now open – and you stop it cold.

So TRF limits autophagy.


The University of Tennessee study doesn’t mention the QUALITY of the food eaten. I suspect most people skipping meals every single day are “rewarding” themselves with junk when they do eat. And so they are missing out on real nutrition, especially fiber. It’s difficult to consume the recommended amounts of fiber if you’re eating only for a few hours every day.


The New Rules to Get the Most from TRF and IF

1. Eat most of your calories as early as possible. You can enjoy a light dinner with your family or friends early in the evening, but power your day with a heavy breakfast and a medium-sized lunch.

2. Don’t neglect actual intermittent fasting.

Give autophagy a chance to regenerate your body. Go without food for 24 hours. Two days a week if you’re overweight, one day if you’re at your correct weight and metabolically healthy.

3. At least 5-6 days per week, eat three meals of HEALTHY food, including lots of fiber. Spread the meals out over a sensible period – 8 to 12 hours depending on your schedule.