Why Severe Calorie Deficits Aren’t Always Good For Weight Loss
Our bodies are very smart when it comes to surviving under harsh conditions. A fantastic — and somewhat infamous example — is adaptive thermogenesis, more commonly known as “starvation mode.”
But what is “starvation mode” and what role does it play in a weight loss journey? Here’s what you need to know.
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 will believe you’re starving. In turn, your body may maintain some of your weight and fat as an attempt to preserve energy, making it harder for you to lose weight.
“Starvation mode” only happens when a substantial caloric deficit is maintained for an extended period. While the exact timeline will vary depending on several factors, one study shows that it can happen after about a week of an extreme daily caloric restriction.
Symptoms of “starvation mode”
There’s just no getting around it. Your body needs calories to work correctly.
If you don’t eat enough, your body will slip into “adaptive thermogenesis,” the scientific term for “starvation mode.” This will slow your whole metabolism down, causing several side effects that will become more and more noticeable the longer you maintain the calorie deficit.
Here’s a quick rundown of the most common “starvation mode” symptoms:
- Lethargy
- Constipation
- Depression
- Inability to concentrate
- Feeling unusually cold
- Reduced appetite
The exact symptoms may vary from person to person but are usually accompanied by a general decrease in your weight loss rate. If you start experiencing any of these side effects, contact a doctor or nutritionist as soon as possible.
“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.
Is intermittent fasting the same as starvation?
No, intermittent fasting is different from “starvation mode.”
First, fasting is only done for a predetermined amount of time, preventing you from going into adaptive thermogenesis.
To put it simply, fasting is a controlled, short-term caloric deficit, while starvation mode is an automatic mechanism that kicks in during long-term, low-calorie diets.
Intermittent fasting can be beneficial to some, providing several health benefits, such as reducing oxidative stress and boosting brain function. Starvation mode, on the other hand, is a sign of damage to your body due to an extended caloric deficit. Remember, consult with your physician before starting any new diet regime, including intermittent fasting, to ensure it is right for you.
There is a lot of anecdotal evidence that intermittent fasting has helped people lose weight alongside a healthy, whole food diet.
What are some of the dangers of prolonged and very low-calorie diets?
The first — and maybe most frustrating — side effect of low-calorie diets is that “starvation mode” can cause your weight loss rate to stall. This can quickly become a catch-22: You eat less because you’re not losing weight, and you don’t lose weight because you’re not eating enough.
Over time, starvation can also cause your muscle mass to decrease due to the overall reduction of calories, weight, and energy. Similarly, your overall body temperature will drop.
A body in “starvation mode” for extended periods is also more vulnerable to illnesses and wounds. The risk of anxiety, irritability, and depression also rises, and you may even develop feelings of guilt and shame surrounding food.
Here are some other long-term “starvation mode” side effects:
- Reduced heart muscle size
- Reduced blood pressure
- Social withdrawal
- Changes in your menstrual cycle
- Impaired immune system
- Weak bones
If you think you may be in starvation mode, we suggest you notify your doctor right away.
Guiding Principles of Healthy Weight Loss Efforts
Let’s face it — losing weight can be challenging. A desperation to lose weight quickly can lead to decisions that may work in the short term but are harmful in the long run.
You should avoid an aggressive approach to weight loss at all costs, as it will often lead you to patterns like yo-yo dieting. Instead, we think the best approach to weight loss is adopting healthy nutritional and lifestyle decisions you can maintain long-term.
This includes exercise, one of the main pillars of weight loss. Moderate exercise can greatly contribute to your losing weight while also keeping your body and mind healthy and active. But even light exercise can help!
You may also want to consider your current eating habits. Do you often find yourself snacking away through the night? Do you eat more when you’re anxious and stressed? Taking note of these habits can help you find common pitfalls in your diet and avoid unnecessary weight gain.
We recommend you keep a food diary to identify any possible patterns. If you’re not too keen on using pen and paper, MyFitnessPal features an extensive food diary with many features to help you start correcting your eating habits ASAP!
Increase Your Metabolic Rate To Lose Weight With a Healthy Diet
If you lose too much weight too quickly, your metabolic rate will decrease, making your weight loss journey much more difficult.
That’s why it’s crucial to follow a healthy weight loss plan that maintains (or even increases) your metabolic rate through exercise and a well-balanced diet. With several useful tools — such as a calorie tracker and food diary — the MyFitnessPal app is the perfect companion for all your weight loss efforts!
Originally published June 24, 2016; updated April 22, 2024