This Doctor Changed His Life with Intermittent Fasting and High Intensity Exercise—You Can Too

Story at-a-glance

  • Intermittent fasting involves cutting calories in whole or in part, either a couple of days a week, every other day, or even daily. It’s one of the most powerful medical interventions for normalizing your weight
  • On the 5:2 intermittent fasting plan, you cut your food down to one-fourth of your normal daily calories on fasting days (about 600 calories for men and about 500 for women), along with plenty of water and tea
  • Many are hesitant to try fasting as they fear they’ll be ravenously hungry all the time. But one of the most incredible side effects of intermittent fasting is the disappearance of hunger and sugar cravings
  • The combination of intermittent fasting with high intensity exercise is a particularly potent combination for normalizing insulin/leptin levels, shedding weight, and optimizing brain function and physical fitness


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

By Dr. Mercola

Is there such a thing as a fast diet? Dr. Michael Mosley, a physician like me, wrote a best-selling book on this subject, aptly called The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting, which answers that question.

As a journalist for BBC in the UK, Dr. Mosley has really helped popularize one of the most powerful medical interventions I've ever encountered for helping people normalize their weight, namely intermittent fasting.

I've previously featured some of his TV documentaries on intermittent fasting and high intensity exercise in this newsletter. In those programs, Dr. Mosley reveals his own health journey, showing how he went from being overweight, diagnosed with diabetes and high cholesterol, to regaining his health.

"My doctor wanted to start me on drugs. But I said, 'I want to see if there's something better and alternative out there,'" he says. "I started exploring, and came across intermittent fasting...

I ended up testing all sorts of different forms of fasting, including alternate-day fasting. Eventually, I came up with something that I called the 5:2 Diet, which is really counting calories two days a week and eating normally the other five days.

I stuck to that for about three months. During that period, I lost about 20 pounds of fat, my body fat went down from 28 percent to 20 percent, and my blood glucose went back to normal.

That was two years ago and it stayed completely normal since... I have to say it's been absolutely life-changing."

Different Types of Fasting Regimens

Intermittent fasting is an umbrella term that covers an array of different fasting schedules. As a general rule however, intermittent fasting involves cutting calories in whole or in part, either a couple of days a week, every other day, or even daily, as in the case of the scheduled eating regimen I use myself.

In his explorations, Dr. Mosley tried a number of these different approaches, including a five-day fast, alternate day fasting (promoted by Dr. Krista Varady), and the 5:2 fast.

The five-day fast was very effective in that he lost weight and improved some of his biomarkers. But it was quite difficult to go a full five days without nearly any food whatsoever. The alternate day fasting also worked, but he found it to be a bit inconvenient.

"And then I came across some work done in England by Dr. Michelle Harvie, which was [fasting] two days a week. I thought, 'I can handle two days a week.' In a way, I kind of combined a number of different techniques together and ended up with the 5:2 plan.

One of my inspirations was the Prophet Muhammad because he had told his followers they all need to fast on a monthly basis for Ramadan but also cut your calories two days a week – Mondays and Thursdays. That's what I did.

I'm not a very religious person, but I do believe that great religions have a lot to teach us, whether it is mindful meditation or indeed some of the benefits of fasting. I think the reason that these ideas persist is there is something very profound about them."

On the 5:2 plan, you cut your food down to one-fourth of your normal daily calories on fasting days (about 600 calories for men and about 500 for women), along with plenty of water and tea. On the other five days of the week, you can eat normally.

Calories Per Day

Yet another version of intermittent fasting, and the one I personally recommend for most people who are overweight, is to simply restrict your daily eating to a specific window of time, such as an eight-hour window. It is more aggressive and, as a result, people will see results sooner.

I too have experimented with different types of scheduled eating for the past three years, and this is my personal preference as it's really easy to comply with once your body has shifted over from burning sugar to burning fat as its primary fuel.

It is important to note that this is not a permanent eating program and once your insulin resistance improves and you are normal weight, you can start eating more food as you will have reestablished your body's ability to burn fat for fuel.

Intermittent Fasting Actually CURBS Your Hunger

Many are hesitant to try fasting as they fear they'll be ravenously hungry all the time. But one of the most incredible side effects of intermittent fasting that I've found is the disappearance of hunger and sugar cravings.

I'm a fellow of the American College of Nutrition and have studied nutrition for over 30 years, and I'd never personally encountered or experienced hunger cravings just disappearing like they did when I implemented intermittent fasting.

Dr. Mosley had the same experience once he began fasting. Others have also contacted him saying they're astonished to realize that hunger no longer dominates their lives; they're back in control. Now, you get hungry because your body needs fuel. But the vast majority of people in the world, certainly in the developed world, are eating foods that severely inhibit their ability to produce lipase and use fat as an energy source. Lipase is inhibited because of high insulin levels, and your insulin rises in response to eating foods high in carbohydrates.

"Absolutely. I think we're just beginning to discover what insulin is capable of –not just in managing blood glucose but also in managing fat deposition and probably its link with cancer and dementia. I think we're just beginning to grasp just how important it is," Dr. Mosley says. When fasting, I recommend paying attention not only to the timing of your meals but also the quality of the food you eat. I believe it's important to eat a diet that is:

  • High in healthy fats. Many will benefit from 50-85 percent of their daily calories in the form of healthy fat from avocados, organic grass-fed butter, pastured egg yolks, coconut oil, and raw nuts such as macadamia, pecans, and pine nuts
  • Moderate amounts of high-quality protein from organically raised, grass-fed or pastured animals. Most will likely not need more than 40 to 70 grams of protein per day
  • Unrestricted amounts of fresh vegetables, ideally organic

Dr. Mosley on Intermittent Exercise

Dr. Mosley is also a proponent of high intensity interval training (HIIT), and recently finished a new book called Fast Exercise.

"The reason I got into high-intensity exercise (and this was three years ago) was because I was making a documentary for the BBC called The Truth About ExerciseI met a professor and he said, 'I can give you many of the benefits of exercise for just a few minutes a week.' I didn't believe him. I did the program; it changed my life."

After that, he began looking into the science behind it, again discovering that there's a huge body of science showing the benefits of HIIT. Dr. Mosley has also started doing a form of high intensity weight training, which is like the strength-training equivalent of HIIT, based on research he found from the University of Texas. But there's also another piece of the fitness puzzle that many are still unaware of, and that is the importance of avoiding sitting. When I first started seeing the studies showing that even fit people had an increased risk of dying if they sat for long periods of time, I couldn't believe it.

I researched it and eventually came across Dr. Joan Vernikos, who's a National Aeronautics and Space Administration (NASA) research scientist. She wrote the book Sitting Kills, Moving Heals. She really drove home the point of how important it is to engage in intermittent non-exercise movement throughout the day. As it turns out, your body needs to interact with gravity in order to function properly.

Ideally, you shouldn't sit down for more than 15 minutes or so at a time. Personally, I set a timer to go off every 15 minutes. Once I got used to the routine of standing up several times an hour, I started adding some simple exercises to it. I've compiled a list of 30 videos for ideas about what you can do when you stand up, to maximize your benefits.

"I'm familiar with the work of Dr. James Levine from the Mayo Institute. He's been shouting, 'The chair is a killer!' for a good 10 years now," Dr. Mosley says. "I met him first about 10 years ago. He had very compelling evidence that you should get off your bottom and move around every 20 minutes or so, even if it's only for a minute, and that being sedentary is itself a killer. It doesn't matter if you go to the gym. You're not going to undo 13 hours of sitting."

Intermittent Fasting Benefits Your Brain

There's exciting research indicating that intermittent fasting can have a very beneficial impact on your brain function, too. It may even hold the key to preventing Alzheimer's disease.

"What really impressed me is when I went to the National Institutes on Aging and I met Dr. Mark Mattson. He's got these genetically engineered mice. They've been genetically engineered so they will develop Alzheimer's or dementia. Normally they'll develop dementia around a year, which is the equivalent of about 40 or 50 in humans.

But when he put them on an intermittent fasting diet – alternate-day fasting diet in fact – they developed it at around two years, which is equivalent to being 90. When he put them on a junk diet, a junk food diet, they developed it at about nine months.

When he looked into their brains, he discovered that the ones who had been on intermittent fasting diet have grown 40 percent new brain cells particularly in the area associated with memory. He identified this thing called BDNF or brain-derived neurotrophic factor, which seems to be driving those changes and also protecting the brains. He's doing this big study in humans at the moment to see if the same thing happens with fasting humans."

Mattson's research suggests that fasting every other day (restricting your meal on fasting days to about 600 calories) tends to boost BDNF by anywhere from 50 to 400 percent, depending on the brain region. BDNF activates brain stem cells to convert into new neurons, and triggers numerous other chemicals that promote neural health. This protein also protects your brain cells from changes associated with Alzheimer's and Parkinson's disease.

BDNF also expresses itself in the neuro-muscular system where it protects neuro-motors from degradation. (The neuromotor is the most critical element in your muscle. Without the neuromotor, your muscle is like an engine without ignition. Neuro-motor degradation is part of the process that explains age-related muscle atrophy.) So BDNF is actively involved in both your muscles and your brain, and this cross-connection, if you will, appears to be a major part of the explanation for why a physical workout can have such a beneficial impact on your brain tissue — and why the combination of intermittent fasting with high intensity exercise appears to be a particularly potent combination.

Eating Like Our Ancestors Helps Optimize Biological Function

One of the arguments for intermittent fasting is that it mimics the way our ancestors ate. They didn't have access to food 24/7, and underwent alternating intervals of "feast and famine." The human body is adapted to this, and research shows that abstaining from food now and then actually optimizes biological function all-around.

"We know, for example, that it's only in the periods when you don't have food that your body goes into a sort of repair mode, because most of the time it's going flat out. Your body's really only interested in procreating, growing cells, always going on and on. But when you go without food for 12 to 14 hours, your body starts to think, 'Well, let's do a little bit of repair now.' Some of the proteins get denatured. New ones get created. Your mitochondria cells originate. There's a lot of fundamental biochemistry, which completely validates this argument," Dr. Mosley says.

"As Dr. Mark Mattson said to me, in terms of the brain work, the time when you need to be smart is not when you have food. Because if you're in a cave and you've got food, you reach out and grab it. You don't have to be clever. The time you have to be smart is when you don't have food. Because then you've got to get up, you've got to get out, you've got a plan, you've got to remember where you left the food before or where you found the berries, and how to hunt. It's actually being without food that makes you smarter."

Optimizing your brain function is yet another amazing benefit of applying these two powerful approaches – intermittent fasting and intermittent exercise. You're actually able to think clearer, get more done, and be far more efficient. It's a phenomenal side effect of following this type of program.

"At the moment, I'm in contact with a group in Ireland who are doing research trying to combine the two approaches, because as far as I know, it hasn't been properly tested together. I believe that together it's going to be much more powerful than separately. It would be nice to have this sort of scientific basis for that [recommendation]."

Finding an Eating Schedule That Works

There are many reasons to implement an intermittent fasting schedule. Adding high intensity interval training and making sure you stand up at regular intervals (several times per hour) can go a long way toward eliminating not only unwanted weight, but also metabolic syndrome and most chronic disease—including heart disease and dementia.

Dr. Mosley and I have both had bouts of diabetes, and close family members have struggled with it as well. Both of us were able to completely reverse our diabetes and regain normal insulin and leptin sensitivity through diet, intermittent fasting, and exercise. Type 2 diabetes is basically 100 percent curable, but you have to give it a sincere effort, and not quit after a few days.

If you struggle with food cravings, especially sugar, know that once you make this shift to burning fat instead of sugar as your body's primary fuel, your hunger for unhealthy foods will vanish, and you will not have to exert enormous amounts of self-discipline to resist unhealthy foods any longer. You will be back in control!

Perhaps best of all, intermittent fasting is not something you have to do non-stop for the rest of your life. I believe that most who are insulin/leptin resistant would benefit from doing it continuously until the resistance resolves. However, once your weight is ideal, and you have no high blood pressure, abnormal cholesterol ratios, or diabetes, then you can have more meals until or unless the insulin/leptin resistance returns.


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