Dr Jason Fung on Ketogenic diet, Fasting and Exercise

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We are talking to Dr. Jason Fung Canadian nephrologist world-leading expert on intermittent fasting and low carb essentially for treating people with type 2 diabetes. 


What is Ketosis?

Ketosis is a natural state when your body is either fasting or has low carbohydrates, so it is essentially when your body has very low carbs which is glucose intake. The brain still needs a source of fuel and it can’t use fat but mostly your body can use fat directly. So fat is triglycerides which are your fat cells. They break down into triglycerides, your liver, your kidneys, and your muscles, they can use the fat from triglycerides directly, but not the brain. So if you’re not eating a lot of glucose, then your liver will produce ketone bodies from the fat, which cross the blood-brain barrier, and then provide most of the energy for the brain. That is a natural state everybody gets confused with ketoacidosis, which is a pathological state. Ketosis is a natural state, when you don’t eat a lot of carbs or when you are fasting. So that is what it is, and you can measure it in the blood, or you can measure it with a breast-tester for example, as a biofeedback measure to say that you are in ketosis, which means your body is mostly burning fat.


So let’s go to the diet itself.  The problem is that I am allowed to eat for 8 hrs, but I am gorging myself for those eight hours. 
 As I said, there are two key components. What you eat and when you eat it. So now you are fixing both. Because you are eating sort of a carb-restricted diet, which is great for weight-loss, and you are combining it with a sort of intermittent fasting, which is clearing a problem plenty. If you eat junk food for those eight hours, it is not going to be good for you. It is better than if you don’t have fasting, but you still have only fixed half the problem, you haven’t fixed the whole problem, the ‘what to eat’ question. It is a question with a lot of different opinions. You must reduce processed food, like sugar, and grain-like flour, and things like that. Bread and cookies and muffin and donuts. Combining a good diet with fasting is very powerful, and that’s why fasting is so important because it works with any diet. Whether you are vegan or carnivore or keto or paleo or whole thirty or whatever, it works with all of those diets, even with your standard American diet. It focuses on something completely different.

My problem as I indicated before is I’ve lost too much weight. My General Practitioner said “okay what were you when you were 20 years old? ”, I said “125 pounds”. He said, “Well that is what you should be”. I looked pretty good. Here I am 77 years old and I weigh 120 now. I am going down. I guess he says I have to eat more.


What do you think?

No, I think it is very good to get down to that weight for sure, but most older people have less muscle mass. So if you compare yourself with age 20 to now, you likely have less muscle mass. Your body weight is a poor indicator of health. Look at metabolic syndrome which is visible in diabetes and high blood pressure and cholesterol. Body weight measure is not seen here.

What is much more closely related to the risk of heart attack is waist circumference. Because that indicates how much abdominal fat or visceral fat you are carrying which is the really dangerous stuff.  So what you are trying to do is get close to half your height, so your waist should be ideally half your height. That is the sort of measure, even if you weigh more or less. It might be because your muscle or bones weigh less. At 20, your bones are heavier and muscles are bigger so you’d likely have weighed more. So if you want to gain weight you really want to increase exercise to try and get some of that muscle mass.

That is where I was going next. What kind of exercise should we be doing?

I think all types of exercise are good for you in different ways. Something I think makes a lot of sense is called high-intensity interval training. I think that is very good. In the 70s and 80s, everybody talked about doing cardio. I think there are benefits to that, but there’s been a bit of swing as well to understand that “hey there are also benefits in doing things like weights and lifting heavy things”. The focus now is more on natural movements rather than isolation. 30 years ago we talked about isolating exercises. That is still important for bodybuilding and definition and so on. But nowadays, you see people doing things like lifting this heavy thing from here to there because it is a natural movement. Free weights, slots, and kettlebells, all of those are sort of mimicking things that we would have done in the past, like carrying a rock. If we were shepherds we might have had to carry a sheep from place A to place B. so that is a natural movement. There’s this move towards doing natural cardio and not just one single muscle group. It is a combination of all those muscle groups together. 

So I walk 4 miles a day, how do you think that fits?

I think these are natural movements and the more you do these movements, the better. If you don’t use it you lose it. This is probably one of the big longevity secrets of all those people in the past, the fact that they just used to walk all the time rather than take cars. You get to a state where the walking itself becomes very enjoyable. The whole point is that you really have to continue to use it. Look at astronauts, for example, you remove gravity and their bones just deteriorate. Their muscles deteriorate, so they have to ride their exercise bicycle, and so on. It’s the same thing. Your body is always in this continual replacement cycle, and if you don’t walk your body loses the ability to walk. We see this in hospitalized patients. If they don’t walk for a week, the rate of deterioration of muscle is rapid. So it’s important to be out there and keep moving, and sometimes that means doing exercise or sports. To be able to build that into your daily routine is actually far more natural, and more enjoyable.



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