Losing weight by cutting calories generally decreases your metabolic rate which hampers further weight loss efforts. Our body tends to maintain a stable weight, the so-called ‘body set weight’.
- Careful scientific studies experimentally demonstrate simple calorie restriction reduces metabolic rate
- On the flip side, deliberate caloric excess increases metabolic rate
- Maintaining weight loss after caloric restriction is difficult if metabolic rate falls
By Jason Fung, M.D., Co-founder of The Fasting Method
We’ve all heard the advice that to lose weight, you need to simply count calories and eat less. We also know that this advice rarely, if ever works. One of the big reasons for its failure is the decrease in metabolic rate, or the number of calories that the body burns each day for energy. While this may be news to some, it’s been a scientifically established fact for decades. It’s worth looking at one of the classic studies published in the prestigious New England Journal of Medicine in 1995, more than 25 years ago to see what lessons can be learned.
Total Energy Expenditure (TEE) and Weight Loss
In this experiment, 41 stable weight subjects, some obese, and some not, were fed a liquid diet of 45% carbohydrate, 40% fat and 15% protein. The amount of ‘food’ given was adjusted to achieve the experimental weight loss or weight gain. In other words, the macronutrient composition of the foods remained constant, and only the amount was varied to achieve the desired weight loss. This is similar to the standard advice to ‘cut calories’ to lose weight. While you can produce weight loss with this method, what are the consequences in terms of total energy expenditure (TEE)? If you frame it in Calories In/ Calories Out terms, the question is what happens to Calories Out when you reduce weight by lowering ‘Calories In’ alone, without changing food composition or things like meal timing?
One group targeted a 10% weight loss and the other group targeted a 10% weight gain. After weight gain, subjects were then returned to their initial weight, and then a further 10% or 20% weight loss was achieved. What happened? Here’s the results in graphical form:
Let’s look at the 10% weight gain group. In response to the weight gain people increased their energy expenditure by almost 500 calories/day. One of the key assumptions of the Calories In/ Calories Out theory is that in response to caloric change, TEE does not change. That is, if you eat more to gain weight, your energy expenditure will remain constant and therefore the extra calories are simply deposited as body fat. This is clearly NOT TRUE. In response to weight gain, the body is trying to burn it off! But this is not the part that interests most people.
What happens when you lose weight by reducing the number of calories? Things start to get really interesting. As weight returns to normal, TEE also returns to baseline. As we move into 10% and 20% weight loss, the body reduces TEE by about 300 or 400 calories per day.
The human body responds to the weight loss induced by calorie reduction by reducing TEE (the number of calories it burns in a day). This will dramatically slow down further weight loss, and strongly encourage weight regain. If you were trying to lose weight by eating less (Caloric Reduction as Primary), this is where you go “WTF?!! OMG, that sucks!”
Let’s put this into a dietary context. Suppose we are at a stable weight and everyday, eat about 2000 calories and burn about 2000 calories. We decide we want to lose some weight so we employ a calorie counting and calorie restriction method, without altering the types of foods or meal timing, just the portions. This is fairly standard weight loss advice given by medical professionals – the misguided dietary technique of portion control. We reduce our daily calorie consumption from 2,000 to 1,700 cal/day.
Initially, body weight goes down, exactly as you intended. Awesome! Our pants fit a little better, and even our mother-in-law says we are looking good. Success! But what happens over time? Our body immediately responds by reducing TEE to about 1,700 cal/day. Because we are using less energy, we might feel cold, tired, miserable and hungry. If you have ever been on a calorie restricted diet – you probably know how that feels. But we’re looking good and losing weight, so hey, it’s worth it.
A few months pass. As energy expenditure drifts downwards, weight loss slows down. Eating 1700 calories/day and burning 2000 calories means a 300 calorie daily deficit. But eating 1700 calories/ day and burning only 1700 calories means no weight loss at all. Determined to beat this thing, we further reduce our calories to 1600/ day. Weight loss begins again, but our body responds by further reducing TEE and once again weight loss stops. This is just math. This happens even if you stick to your calorie restricted diet perfectly.
But the lower TEE means you feel colder, hungrier and more tired, which hardly seems worth it without any weight loss. Discouragement sets in. Tired of feeling so lousy, we increase our caloric intake a touch – to 1800 calories/day. More than the current 1600, but less than the original 2000 calories/ day. Because TEE is only 1600 calories and you are eating 1800 calories, weight starts to come back on.
We feel we have failed ourselves. We think that it is our fault. Our doctors, dieticians, and other medical professionals silently criticize us for ‘failing’. Others silently condemn our lack of ‘willpower’, and offer meaningless platitudes but no explanations. Sound familiar? Yeah, I thought so.
But in truth, the failing was not ours. The portion control diet is virtually guaranteed to fail. It has been scientifically and experimentally proven many times over the last 100 years. The only reason we think that it works is because everybody – the doctors, the dieticians, the ‘scientists’, the media – has convinced us that it is all about calories. That is, the only factor about food that matters for weight gain is the number of calories you eat in a day. Nothing could be further from the truth.
How much body fat we carry acts like a thermostat. In your house, you set a desired temperature – usually room temperature, approximately 22 degrees Celsius. If your house gets too hot, the thermostat turns on the air conditioner to cool it down. If the house gets too cold, the thermostat turns on the heat to warm it up. The end result is that the house maintains a relatively stable room temperature.
The body sets a Body Set Weight (BSW). If you eat too much, (too many calories in), your body will increase the number of calories burned to compensate (TEE increases). If you eat too little and lose weight, then your body will reduce the number of calories burned (TEE decreases). Both will return the body closer to its BSW. No wonder it is so hard to keep the weight off!
So the most important question for successful long term weight loss is not “How can I reduce my calorie intake?” The question we want answered is “How can I lower my body set weight?” As with everything in the body, our weight is controlled by our hormones, not counting calories.