On The Table

A collection of knowledge-based articles to inspire overall wellness.

What Happens If You Lose Weight Too Fast?

Rapid weight loss is often a desired goal but can actually do way more harm than good—here's how.

What Happens If You Lose Weight Too Fast?

Depending on what stage of life you’re in, fast weight loss might sound like a dream. However, if you lose weight too quickly, it can turn into a dangerous nightmare. 

Losing weight may be more sustainable in the long term if you seek weight maintenance instead. Learn about the side effects of rapid weight loss, serious risks to consider, and more ahead!

What Is Considered Rapid Weight Loss?

Safe weight loss is generally losing 1-2 pounds per week. That may not seem like much, but small, significant shifts can add up. For example, you can safely lose 10 pounds in two months

Of course, not all weight loss is intentional. Unintentional weight loss, sometimes called unexplained weight loss, is considered a loss of more than 5% body weight (or 10 pounds or more) in 6-12 months. This means that even a seemingly small amount of weight loss may be a signal of a bigger problem, especially if you’re not trying to lose weight. 

Common Risk Factors of Rapid Weight Loss

While seniors are most susceptible, unexplained weight loss can also occur due to other underlying factors, such as: 

• Dental issues or dysphagia (swallowing difficulty) 
• Digestive disorders (i.e. celiac disease, Crohn’s disease, ulcerative colitis)
• Disease or chronic disease (i.e. cancer, diabetes)
• Eating disorders 
• Excessive exercise) 
• Hormone fluctuations or imbalances (i.e. Addison’s disease, thyroid disorders)
• Immune system impairments (i.e. AIDS)
• Infection (i.e. parasite)
• Memory disorders (i.e. dementia, Parkison’s disease) 
• Mood disorders (i.e. anxiety, depression) 
• Side effects from medication 
• Substance abuse (i.e. alcohol, drugs) 

In terms of calories, most women should be eating at least 1,500 calories per day and men should be consuming about 2,000 calories per day. If you’re eating less than what is recommended, weight loss will result, but only because you are losing muscle mass (not body fat). You may also be losing bone mass and water. 

Individual calorie needs may vary, which is why it is important to work with a dietitian (a professional qualified to meet your health goals while ensuring nutrient adequacy). Athletes, for example, may need to fuel their bodies with more calories to maintain a certain weight and provide enough energy for their daily activities. 

5 Dangers of Losing Weight Too Fast

The side effects of losing too many pounds per week may seem subtle at first, but can quickly become serious. Here are five major problems that can arise when the weight comes off too fast. 

1. Loss of Muscle 

If you’re losing weight too quickly, you may be losing some body fat. However, it’s more likely that you’re losing muscle. Building muscle helps enable the body to burn calories (such as during exercise). When you lose muscle mass, your body may have a harder time keeping up with daily activities. 

Alternatively, experts suggest aiming for losing no more than 1-2 pounds per week while eating a healthy diet and engaging in appropriate exercise activities. This allows your body to burn fat without losing muscle mass. In other words, you’ll build muscle while shedding fat the most sustainable way. 

2. Hair Loss

It’s no secret that healthy hair and nails are an extension of a good diet. However, most people are unaware that fast diet tactics can lead to hair loss. 

Rapid weight loss can lead to a type of hair loss condition called acute telogen effluvium (TE). Restrictive diets lasting as little as 3 months can trigger TE. Common causes of hair loss linked to diet include: 

• Calorie restriction
• Crash dieting or fad diets (i.e. keto) 
• Nutrient deficiency 
• Protein malnutrition 
• Weight loss surgery 

Since many people wanting to lose weight quickly are aware of body image, it makes sense why hair loss could be concerning for this crowd. Luckily, understanding the risks of rapid weight loss can help you avoid unpleasant effects (like hair loss). 

3. Frequent Fatigue 

Fatigue is a symptom tied with many disorders, but can also be tied to a restrictive diet. Beyond a feeling of tiredness, fatigue stands in the way of functioning day-to-day and can cause errors, accidents, and a decrease in quality of life. 

Likely due to calorie-restrictive eating practices, (not eating enough calories a day), a low-calorie diet can contribute to the fatigue you’re feeling. While fatigue may seem like a vague symptom, it’s actually a clear signal from your body that it’s not getting what it needs. 

4. Nutrient Deficiency 

The human body needs both macronutrients (protein, carbohydrates, and dietary fat) and micronutrients (vitamins and minerals) each day to function properly. When you aren’t getting enough calories, you’re likely not getting enough nutrients or fluids either. Malnutrition and dehydration can quickly follow if you aren’t eating enough calories each day. 

Electrolyte imbalance, a condition that occurs when your body has either an insufficient or excessive amount of certain minerals, can also happen with rapid weight loss. Found in blood, tissues, and urine, electrolytes are critical compounds that help support fluid balance in the body. 

The gallbladder, an important organ in the process of water and electrolyte absorption, can particularly be affected in cases of rapid weight loss. In fact, very low-calorie diets (VLCDs, which are around 800 calories per day) are linked with increasing the risk of gallstones. Gallstones are not only painful but may even require surgery or cause additional nutritional problems due to nausea or vomiting. 

5. Hormone Imbalances

You’ve probably already heard that hormones are the chemical messengers of the body. With rapid weight loss, imagine those messages turning into emergency memos, alerting and alarming the body. Such swift changes can cause your body’s metabolism to shift into survival mode, which isn’t helpful when you’re trying to thrive. 

Hunger hormones, like ghrelin and leptin, will likely be the first to be affected. After that, hormones in the gut that affect digestion and nutrient absorption, like cholecystokinin (CCK), may also experience some changes. Stress hormones like cortisol may also be affected by excessive calorie restriction or fad diets like intermittent fasting. 

Serious calorie restriction can also cause menstrual irregularities in women. Namely, a condition called amenorrhea (loss of normal menstrual cycle) can occur and is cause for concern. Levels of the sex hormones estrogen and testosterone can also change in a way that’s not helpful to the body. 

Essentially, weight loss that occurs too quickly can confuse the hormones in your body. Slow, sustainable changes are more likely to provide the balance your body needs and keep those chemical messengers in check. 

The Last Word on Losing Weight Too Fast

When choosing a weight loss plan, it’s important to select something sustainable. Losing weight too quickly can cause serious problems for your health, like nutrient deficiencies and muscle loss. Slow and steady diet practices really do win the race when it comes to weight loss. 

Related Questions

How fast is too fast to lose weight?

Losing more than 1-2 pounds per week may mean you’re losing weight too quickly. If you’re not trying to lose weight, an unexplained loss of more than 5% of body weight (or 10 pounds or more) in 6-12 months is considered a cause for concern. 

What happens if you lose weight too fast?

If you’ve lost weight too quickly, you can cause your body to experience other health problems such as fatigue, hair loss, hormone disruption, precious muscle loss, and nutrient deficiency—just to name a few. These problems can cause long-term issues that impact your overall health and quality of life. 


Ansel K. 5 Things That Happen to Your Hormones When You’re Trying to Lose Weight. Eatingwell.com. Published September 2021. 

Azzolino D, Arosio B, Marzetti E, Calvani R, Cesari M. Nutritional Status as a Mediator of Fatigue and Its Underlying Mechanisms in Older People. Nutrients. 2020;12(2):444. 

Cleveland Clinic. Electrolyte Imbalance. My.clevelandclinic.org. Published August 2022. 

Cleveland Clinic. Is It Bad to Lose Weight Too Quickly? Health.clevelandclinic.org. Published October 2021. 

Cleveland Clinic. Unexplained Weight Loss. My.clevelandclinic.org. Published August 2018. 

Ellis E. Staying Away from Fad Diets. Eatright.org. Published March 2019. 

Kaufman C. 4 Ways Low-Calorie Diets Can Sabotage Your Health. Eatright.org. Published January 2021. 

Mayo Clinic Staff. Unexplained weight loss. Mayoclinic.org. Published August 2022. 

Kubala J. How Are Weight Loss and Hair Loss Related? All You Need to Know. Healthline.com. Published February 2021.