A client who participated in the 14 Day Sugar Challenge asked me why you stop losing weight on low calorie diets. She'd been using MyFitness Pal which calculated her caloric intake for her weight loss to be 1300 calories a day. The first few months she was losing weight, then nothing. No movement on the scale for weeks. She couldn't understand why she wasn't losing weight.
Everything we're told about weight loss is that you have to eat fewer calories to lose weight. But the truth is, weight loss is not as simple as "calories in, calories out." In fact, I did my research paper on "calories in, calories out" for my nutrition capstone. It's much more complex than this, and today I'll cover one reason why.
Why You Stop Losing Weight On Low Calorie Diets
When you eat really low calories 1200-1300 calories for a period of time, it changes your metabolism. Get ready for some nerdy nutrition!
Metabolic Rate Lowers With Low Calorie Diets
Studies show that as an individual lowers their caloric intake, the body adapts by lowering resting metabolism (1). The body becomes more efficient in utilizing the reduction of calories it receives to preserve fat loss. A lower metabolism is exactly what you do not want when you're trying to lose weight!
This adaptation is like what the body does with exercise. When you do a certain activity over and over, muscles remember the activity and start doing them more efficiently. Think of your metabolism as a muscle. If you eat too few calories, your metabolism adapts by slowing down.
While a reduction in calories may initially yield weight loss, it’s only a matter of time before you reach a plateau and the scale stops going down. One study showed that resting metabolic rate (RMR) adjusts in non-obese people with modest physical activity by month 3 (2).
How Exercise Affects Metabolism
Additionally, researchers who investigated the approach of the Biggest Loser concluded exercise didn’t prevent this slowing of resting metabolism, it only preserved muscle (3). This may answer why many individuals regain weight after weight loss because as shown, metabolism slows with calorie restriction so when a person begins eating more they begin to regain weight. Calories in, calories out cannot outsmart the intelligence of metabolism.
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Weight Loss Is Complex
Weight loss is more complicated than math. Genetics, food quality, macronutrient balance, hormones, lifestyle, are just a few things that can greatly impact the ability of a person to lose weight.
Further, calorie expenditure is highly variable - in a person and in food. The calories you see on food labels vary by 20% and the calories that apps estimate for your body are estimates too. But no matter how precise they were, it wouldn't change the effect on metabolism.
How Do You Lose Weight Then?
There are a couple methods, but I generally recommend people start by reduce calories slightly then as time goes on add them back gradually, and/or cycle macronutrients to keep metabolism guessing. What you never want to do is reduce calories even more because that can have a detrimental effect on hormones which play an important role in weight loss.
This is why it's important to consult an expert before losing weight. To ensure you're doing it the right way that's safe and healthy for you. Remember, apps are useful but not the bible.
(1) Metabolic slowing with massive weight loss despite preservation of fat-free mass. (n.d.). Retrieved January 22, 2017, from http://www.ncbi.nlm.nih.gov/pubmed/22535969
(2) Effect of calorie restriction on resting metabolic rate and spontaneous physical activity. (n.d.). Retrieved January 14, 2017, from https://www.ncbi.nlm.nih.gov/pubmed/18198305
(3) Effect of Calorie Restriction on Resting Metabolic Rate and Spontaneous Physical Activity. (n.d.). Retrieved January 17, 2017, from http://onlinelibrary.wiley.com/doi/10.1038/oby.2007.354/full