Watch this informative talk on the utility of fasting for health by nephrologist Dr. Jason Fung. Below the video, I have placed a summarized transcript of the key points of his talk with the links to the articles reviewed in the talk.
Fasting for weight loss: Unlimited Potential
Reduced calorie diets don’t work, e.g. The biggest loser diet. Cut calories in, cut calories out.
The Biggest Loser Study
J Clin Endocrinol Metab. 2012 Jul;97(7):2489-96.
Metabolism slow down
The reason the “calories in and calories out” model such as in the biggest loser doesn’t work is because the metabolism starts to slow down.
The first diagram in the article shows the weight loss, much of it is from fat, not muscle. The second shows the decreased metabolism.
The average decrease in metabolism is >700.
Say your metabolism rate slows down from 2000 calories per day to 1200 calories. And then you find yourself eating 1500 calories. That is still 500 less than you used to it, but you will be eating 300 calories more than you are burning per day and you will gain weight.
You feel tired, cold, weak, but you are gaining weight!
When you start eating a low-calorie diet, your body fights back and lowers the metabolism rate.
Bariatric surgery, which is also extreme, doesn’t seem to have this problem of your metabolism slowing down. For bariatric surgery, the metabolism bounces back up and really doesn’t slow down.
Article he cites:
J Clin Endocrinol Metab. 2012 Jul;97(7):2489-96.
Title: Metabolic slowing with massive weight loss despite preservation of fat-free mass. https://www.ncbi.nlm.nih.gov/pubmed/22535969
We’ve known about this metabolism slow-down for over 100 years.
This leads to poor advice from doctors to patients. When it doesn’t work, doctor’s blame patients for the failure.
The reason for the discrepancy? The answer is in knowing what happens when you eat.
We Eat Food > Insulin gets secreated > Store Sugar in Live. Produce Fat in Liver.
When you don’t eat, no insulin is secreted, you burn calories, and then you start burning fast. The process is reversed.
No food (Fasting) > Decrease insulin > Burn stored sugar in liver. Burn fat in liver.
It’s like you have a fridge and a freezer. Or a wallet with money and a bank account.
The other models are wrong because they have a one-compartment model where all energy is stored in one account. You can put energy in and take it out from the same place. But that’s not how it works.
Insulin controls the movement of fat into and out of the cells.
If you have a lot of insulin but lower your calories, the body will not burn fat because insulin prevents fat from being burnt. What your body will do to protect itself is to lower your calories out by lowering your metabolism. The body can’t simply let you die by keeping your metabolism high when it can’t access the fat.
If you look at the women’s health initiative, a 50K women study, they reduced calories by 350 per day for 7 years. They estimated that people will lose 30lbs per year. In 7 years, they expected 210lbs. How much did they lose? Nothing.
Because their body lowered the metabolism.
Not that the laws of thermodynamics aren’t being broken. Energy in and energy out is being respected. But what is important here is the compartmentalization of energy that is happening and the role that insulin is playing.
The problem is what the insulin is doing.
Graph from research by Kevin Hall at the NIH shows that during the first few days, glycogen is burned off, then fat takes over. Protein is burned only briefly and then goes down.
Fasting doesn’t cause people to burn muscle. You store energy as fat and when you don’t have energy and there is no insulin, you burn the fat. You don’t burn protein.
Fasting and low carbohydrate diet empties the fridge (i.e. the glycogen storage). It is the most efficient way. Fasting lowers insulin and allows room for us to access fat.
How do you lose weight? Just don’t eat. If you don’t eat, you will lose weight.
We are built to withstand periods of no food.
Myth – Fasting will put you into starvation mode.
That’s not true, because starvation means that your metabolism reduces to such an extent that you will regain weight.
Fasting doesn’t put you into the starvation mode. Actually, reducing your calories without reducing insulin will lead to a reduction in metabolism, which could put you into starvation mode.
Metabolic changes over 4 days of fasting.
Citation: Am J Clin Nutr. 2000 Jun;71(6):1511-5.
Real title of study: Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine.
He has graphed the data that he wants to show on the chart.
Notice that the Resting Energy Expenditure goes up, not down. That’s what is expected.
Explanation? Suppose you are cave man, if your fasting, your body wants to give you energy so that you can go out and get something to eat and fill up the refrigerator. If it makes you tired and slows down, you are more likely not to find something and then die.
Alternate day fasting
Am J Clin Nutr 2005; 81:69-73
Another similar article:
Title: The effects of modified alternate-day fasting diet on weight loss and CAD risk factors in overweight and obese women
Conclusion: “These findings suggest that short time alternate day fasting is a viable dietary option to help obese individuals lose weight and decrease some CAD risk factors. More and longer-term studies in human subjects are needed to support this important result.”
Again, during fasting, you don’t burn any protein/muscle.
Diagram from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2279566/
It shows that the urea doesn’t go up during fasting.
You can do 70 days of alternate day fasting as in this study:
Obesity (2010) 18, 2152-2159
In this study as well, fat mass goes down but the fat-free mass remains the same. Again, you don’t lose protein when you fast.
Will fasting work? Absolutely. It will work. Absolutely.
Now, is it easy to do? No.
Men and women the same, they will lose weight. There is no weight plateau.
Drenick, Am J Public Health Nations Health. 1968 Mar; 58(3): 477–484.
Page 478, the top diagram shows that both men and women lose weight.
Most people can fast!
“Fasting has unlimited power..”
It frees us from the chains that bind us!