The Fallacy of the Underfed Metabolism
Have you heard eating too little would put your body in “starvation mode” and cause it to start storing fat? Or if you consume less than 1,200 calories per day your metabolism will stop?
These ideas are common in the dieting world. But are they true? Believe it or not, the answer is no.
Every single person who cuts calories to lose weight sees a drop in resting metabolic rate (RMR), the amount of energy expended daily at rest. RMR is not to be confused with total-daily-energy expenditure (TDEE). RMR is part of TDEE – about 70% to be exact. Seventy percent of the calories you burn in a day don’t entail moving a muscle. So what about the other 30 percent?
Twenty percent of your TDEE comes from movement, including everyday activities and exercise. The remaining 10 percent comes from the energy it takes to digest the food and drink you consume.
A Real-Life Client Case Study
One of my clients, Jane, is in her mid-50s, 5’6, and 160 pounds. She’d lost 10 pounds in seven weeks but had been stalled for the two most recent weeks.
After cutting calories to lose weight, her RMR slowed: This is normal, natural and to be expected. It slows to conserve fat, fuel, and resources. The body doesn’t know if it is running out of available food, so it slows down to protect what it considers precious fat reserves. Some people see a five percent drop in RMR when losing body fat while others will see a 25 percent drop, depending on genetics, previous diet attempts, food quality, and source and level of caloric deficit.
Jane was eating 1,100 calories per day while she was losing weight. Once her weight stalled, she cut her calories to 800 per day. After two weeks of holding steady at about 800 calories per day, she asked for my help when her weight hadn’t budged.
She said: “Maybe I need to eat more to jumpstart my metabolism and lose weight.”
I asked her to get her RMR checked at a local university, which was measured at 1,083. This means she needs 1,083 calories per day without moving or eating.
A quick calculation on the ShapeUp.org website says her RMR should be about 1,291 calories/per day. Some quick math (1291-1083 = 208: 208/1291 =.16) says her RMR slowed about 16 percent from the projected base. First, that is well within the normal range of RMR slowdown with caloric restriction. And second, her metabolism wasn’t broken.
So why isn’t her weight moving?
MOST often, the problem with weight stalls is too little attention paid to nutrition, plus licks, bites, tastes, and sips that go unaccounted for (food creep). Jane, however, was eating a TRUE 800-calorie plan, give or take 10 percent.
SHOULD Jane be losing weight by eating 800 calories per day? Yes.
On top of being a stellar eater and record keeper, Jane was also exercising 280 minutes per week (40 minutes per day). That is ideal for the everyday person wanting to be healthier and leaner.
Because we know her actual RMR and how much she’s exercising, we can do the math to see what she needs to maintain her weight and how much weight she should be losing if she’s eating 800 calories per day.
RMR + (value of exercise in calories/day) + (at least 10% add-on to RMR for daily movement) + (10% add-on to RMR to digest food) = TDEE needs to MAINTAIN.
1,083 + (40×6 = 240) + (1,083/10 = 108) + (1,083/10 = 108) = 1,539 calories/day to maintain.
What should she have been losing strictly by the numbers?
1,539-800=739. By eating 800 calories per day, she created what should have been a 739-calorie deficit. That multiplied by seven days in a week equals a 5,173-calorie deficit in a week. This is equivalent, loosely, to 1.5 pounds of body-fat loss per week. For every 3,500 calories of deficit (approximate calories in a pound of fat), we lose about one pound of body fat. 5,173/3,500 = 1.5
If Jane were involved with any other diet or weight-loss programs, she would have been told she was foolish for eating below her RMR and/or that she stalled her metabolism. She would have been prescribed a 750-1,500 calorie increase to “restore her metabolism,” so she could later try losing weight with a more “sensible” caloric deficit. And that would have been the exact wrong thing to do.
If she bumped her calories to 1,000/day, her RMR would need to rise to 1,283 to stay the status quo. Why? If she was eating 200 additional calories, her RMR would have to jump 200 calories per day just to break even. If she increased her calories to the dietetic gold standard of 1,200/day, her RMR would need to increase to 1,483/day. Worried about a too-slow metabolism? Want to eat more to “restore” it? For every additional calorie you consume, your RMR has to rise equally, or you will gain weight rather than lose it.
If you’re not losing weight eating 800 calories a day and exercising 280 minutes a week, the issue isn’t RMR or the numbers on a paper – but the actual numbers being eaten, the actual exercise minutes and effort, OR the fact that too many people consider a five- to seven-day stagnation on the scale a weight stall. I don’t consider a true stall to occur unless 10-14 days have passed with no change. Beyond two weeks? SOMETHING needs to change.
Strictly by the numbers, it makes no sense that anyone overweight eating 800 calories a day, and exercising 280 minutes should be in maintenance mode.
But Jane was stuck. It could have been any number of things unrelated to a broken metabolism and under-eating. I discovered the answer during a short phone call.
Jane mentioned she’d had a urinary tract infection and had been on antibiotics. When she felt healthy again, with proper bowel function (her prescription caused constipation) and energy, she increased her calories to 1,100 per day. This coincided with getting clear from the effects of the infection and antibiotics. At first, she thought her weight started moving because she increased her calories. But it was just a coincidence.
The reason her weight stalled was she had an infection. In addition, she was put on an antibiotic that causes water retention AND constipation, which wasn’t an issue in her early weight-loss success.
Once her body was clear, the issues causing water retention and constipation were alleviated and the scale could, once again, show the true results of her efforts.
To add things up:
- I am not a fan of undereating but it has nothing to do with breaking metabolisms. It has to do with the potential for nutrient inadequacies when calories are too low, unnecessary loss of precious muscle, and how my clients feel mentally, physically, and emotionally if they eat too little.
- I am a fan of eating the maximum calories and nutrients one can eat to achieve desired goals. If someone can eat 2,000 calories a day and lose the body fat they want and achieve their ultimate vision, I am thrilled.
- If 600, 700, or 800 calories a day was a true “metabolism killer,” we wouldn’t have the University of California and hundreds of other bariatric centers promoting 300-600 calorie days for months post-surgery. According to the University of Michigan Adult Bariatric Surgery Program “The average weight loss following gastric bypass surgery is approximately 5-15 pounds per week for the first 2 or 3 months with a gradual tapering off to about 1-2 pounds per week after the first 6 months or so.” Although I’m against bariatric surgery except as a last resort, you cannot argue against the results. They are, in large part, due to the incredibly small volume of food the successful patients consume. Do their metabolisms slow? Yep. And they lose a ton of weight anyway-as we’d expect they would.