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Intermittent Fasting Benefits

October 15, 2019  |  By: Whitney E. RD

Intermittent fasting, also known as time-restricted eating, has become extremely popular in the health and fitness world. But does it have any true health benefits or is it just another fad? On this episode of The Sitch, we’re exploring the science behind intermittent fasting and talking about how to do it right.

Intermittent fasting has quickly become a popular dietary practice. Social media is buzzing with caveman wannabes spouting the benefits of consuming all of their daily calories (mostly collagen) in a 4-hour window between their morning polar bear swims and evening CBD doses.

Proponents proclaim intermittent fasting helps with weight loss, athletic performance, disease prevention, and improved cognition.

But are the benefits worth the hype? And are the types of fasting regimens that biohacker bloggers support in line with scientific research? Let’s explore.

First, let’s talk about what fasting and intermittent fasting actually are and how they work.

WHAT IS INTERMITTENT FASTING?

Fasting is the practice of abstaining from food for a set period of time. Intermittent fasting is a type of fasting where you alternate between shorter periods of eating and fasting, usually between 12-24 hours. Although the average American continuously eats throughout the day and often late into the evening, allowing the body time to rest between meals (aka fasting) is just how we should normally operate.

In the simplest terms, during feeding, our body increases processes related to growth and reproduction. When we fast, our body slows growth and instead focuses on rest and repair. Fasting is believed to upregulate processes in the body like DNA repair and programmed cell death (also known as autophagy) resulting in disease prevention and increased health and lifespan.

Research on fasting and caloric restriction has been going on for a while and the benefits in animals are pretty much indisputable. Studies in rodents show that those who are chronically calorically restricted live on average 50% longer than those fed a normal diet and are free of common diseases. Meanwhile, humans who lack certain genes that are turned off during fasting have been shown to have extremely low rates of chronic diseases like cancer and diabetes.

However, clinical trials of fasting in humans only started in the past decade, therefore, while fasting is an ancient practice and there’s a lot of research going on right now, there’s still a lot to learn.

Let’s talk about the different types of fasting.

TYPES OF FASTING

Periodic fasting refers to fasting that lasts for several days or more when only water is consumed. The fasting-mimicking diet, a 5-day protocol, which I tried and did a YouTube video on, is a subtype of this kind of fasting.

Intermittent fasting refers to continuous bouts of fasting, usually in the range of 12 hours to a full day.

There are a few different types of IF regimens.

16:8 Fasting Regimen

The 16:8 regimen has participants fast for 16 hours and eat during an 8-hour window. Those who follow this protocol often skip breakfast and eat somewhere between noon-8 pm. This type of fasting is also known as time-restricted eating. Variations allow for greater or smaller eating windows.

Alternate Day Fasting

Alternate day fasting is just what it sounds like. One day on, one day off. A modified version of this allows for the consumption of about 25% of a person’s daily needs on fasting days.

The 5:2 Diet

The 5:2 diet, aka the FastDiet, has participants eat normally 5 days a week and then fully fast or eat only 25% of daily needs on 2 nonconsecutive days a week.

BENEFITS OF FASTING

There’s no doubt that fasting improves cardiometabolic health. Research shows that fasting in general results in weight and fat loss, improved insulin sensitivity, reduced glucose and insulin levels, lower blood pressure, improved lipid profiles, and reduced markers of inflammation and oxidative stress. This is not surprising, as weight loss from traditional caloric restriction can also produce these results.

The question is – does fasting have any unique benefits or increased benefits over simple calorie-cutting?

Well, as far as weight and fat loss, no. Research shows that when people eat the same amount of calories, they lose the same amount of weight – no matter what the time period. Studies show that intermittent fasting does not increase metabolism or result in more calories burned. The reason people tend to lose weight with intermittent fasting is because they typically eat fewer calories in their time window than they would normally.

This may be because fasting has been shown to decrease the hunger hormone, ghrelin, which doesn’t occur when people are on normal calorie-restricted diets. This one reason why intermittent fasting may be preferable for weight management over traditional diets.

However, studies have shown that fasting may have benefits independent of weight loss. For athletic performance, one study of time-restricted eating in healthy men showed improvements in strength and endurance and an increase in lean body tissue, despite a decrease in food intake. For diabetes, one epidemiological study in women found that for every 3-hour increase in nightly fasting, women had a 20% reduced risk of elevated HbA1c, a marker of type II diabetes. And for cancer, a study in women with early-stage breast cancer found that those who fasted for less than 13 hours from their last meal of the day to their first meal had a 36% increased risk of breast cancer recurrence.

The timing of a fast may be important. Studies show differences in outcomes when food is consumed earlier in the day vs. later. One study of early time-restricted feeding in men with prediabetes – where the participants ate during a six-hour window and stopped eating before 3 pm – showed improvements in insulin sensitivity and beta cell functioning, lowered blood pressure, and decreased appetite in subjects, all without weight loss.

Meanwhile, studies of late time-restricted feeding, where all meals take place after 4 pm, have showed either no results or worse results. One study in healthy normal weight adults showed impaired glucose tolerance and increased levels of the hunger hormone ghrelin when participants consumed all of their daily calories at one meal between 4 and 8 pm versus at three meals throughout the day. This is likely due to our circadian clocks. Yes, clocks, plural. Every cell in the body and all of our physiological processes operate in alignment with each other in a harmonious 24-hour rhythm tied to the time of day. Insulin sensitivity, beta-cell functioning, and metabolism are all at their peak in the morning, and they decrease as the day goes on. Therefore, fasting in the morning and eating in the evening puts us out of sync with this system and – as demonstrated by research – results in fewer or no benefits from fasting.

So it appears that fasting, regardless of weight loss, does provide health benefits when it’s done right – in sync with our body’s natural rhythm. But are there any negatives or people who shouldn’t fast?

RISKS OF FASTING/PEOPLE WHO SHOULD NOT FAST

Patients with certain medical conditions like diabetes may be at risk of complications from fasting caused by hypoglycemic events.

Fasting also may be inappropriate for people who need to consume medication with food at a specific time of day.

Pregnant women also should not fast as fasting may lead to weight loss which could jeopardize fetal growth.

People who have suffered from eating disorders are also advised to avoid fasting as it may trigger relapse or bingeing episodes.

Finally, there’s the issue of sustainability. I’ve discussed in previous videos how diets, in general, are unsustainable. The majority of people who lose weight dieting end up gaining it all back – and then some. So far the fasting research isn’t much better.

In the longest study to date of intermittent fasting – one-year doing alternate day fasting – there was a 38% drop out rate, which was higher than a group doing traditional caloric restriction. However, ADF is considered one of the hardest fasting regimens – other than multiple day water fasts.

Obviously more long-term studies are needed to determine whether other types of fasting would easier to stick to in the long run.

WHICH TYPE OF FASTING IS BEST?

Here’s the thing – there are so many different types of fasting and the clinical trials all have so many different variables that it’s hard to draw firm conclusions about which type of fasting is best.

What we do know – caloric restriction and fasting can prevent disease in animals and extend lifespan. In humans, both result in weight loss and potentially metabolic benefits.

Any type of fasting is probably beneficial if it’s done properly and people are able to stick to it; it’s certainly better than eating round the clock.

Research shows that shift workers, who work odd hours and often eat when our bodies are primed for sleeping, may have a higher risk of breast cancer, cardiovascular disease, and diabetes.

Personally, I recommend what I call “common sense fasting” – simply not eating between dinner and breakfast. That may be a 12-hour window for some, longer for others. It depends on your lifestyle.

I also recommend periodic fasting 1-2 times a year for general health, or more frequently to address a specific disease concern – talk to your doctor about it.

And finally – exercise! People who exercise have a much better chance of keeping weight off.

Bottom line: if your only goal with fasting is weight loss – it’s debatable whether it’s the best option. If you’re interested in improving your overall health and hopefully reducing your risk of chronic disease, it’s a helpful addition to your toolbox.

And that’s The Sitch!

For more info on fasting, check out my interview with Dr. Valter Longo, Director of the University of Southern California’s Longevity Institute.

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