Why a severe calorie deficit isn’t always good for weight loss (previous post)

Our bodies are very clever when it comes to surviving in harsh conditions. A wonderful and somewhat infamous example is adaptive thermogenesis, often referred to as “starvation mode”.

But what is “starvation mode”? And what role does it play in your weight loss journey? Here’s what you need to know.

Symptoms of “starvation mode”

There’s no getting around it. Your body needs calories to function properly.

If you don’t eat enough, your body goes into “adaptive thermogenesis”, which is the scientific term for “starvation mode”. This slows down your entire metabolism, leading to side effects that become more and more pronounced the longer you maintain a calorie deficit.

Here’s a quick overview of the most common “starvation mode” symptoms:

1.lethargy
2.constipation
3.Depression
4.Inability to concentrate
5.Feeling unusually cold
6.Loss of appetite

The exact symptoms may vary from person to person, but are usually accompanied by a general decrease in the rate of weight loss. If you begin to experience any of these side effects, contact your doctor or dietitian as soon as possible.

Is “starvation mode” a real phenomenon or just a myth?

The concept of starvation mode is simple: if you don’t eat enough, your body thinks you’re hungry. In turn, your body may maintain a certain amount of weight and fat to conserve energy, making it harder for you to lose weight.

“Starvation mode” only occurs when you maintain a large calorie deficit for an extended period of time. While the exact timeline will vary depending on several factors, one study suggests that this may happen after about a week of extreme daily calorie restriction.

“Starvation mode” and its impact on weight loss

When in “starvation mode”, your metabolic rate may decrease significantly, especially if you lose too much weight too quickly. Metabolic rate refers to the number of calories you burn daily, making it crucial to the caloric intake and outtake formula.

The exact numbers will vary depending on how fast you lose body weight, but a good rule of thumb is that adaptive thermogenesis will kick in after about one week of severe caloric restriction, which is restricting total daily energy intake to be below basal metabolic rate (BMR).

BMR is the amount of energy in calories your body needs just to do the basics—breathing, circulating blood, regulating body temperature, and repairing cells—when at rest. Think of it as the calories you’d burn if you stayed in bed all day. It’s affected by things like your age, sex, weight, height, body composition, and even genes. 

And, according to registered dietitian and scientific advisory Scott Keatley, 1,200 calories is the absolute bare minimum a human body needs daily. (Aka, the lowest BMR you can have). “Even someone under 5 feet and 100 pounds needs more if they do anything beyond blink,” he says.