You might think that the key to weight loss is eating less and moving more. If a modest calorie deficit is effective for weight loss, a bigger calorie deficit must lead to even better results. But the truth is that eating too little can hurt your weight loss efforts, especially over the long run.
When you eat too little, the body naturally responds by increasing hunger and altering satiety hormones, while also lowering metabolic rate, trying to restore balance and protecting you against rapid weight loss. A diet may, therefore, provide short term gain but at a long-term cost.
The Minnesota Starvation Experiment
The 1950 Minnesota Starvation Study revealed the profound effects of severe calorie restriction. In the study, participants’ calorie intake was reduced by 40%, leading to an average weight loss of 25%. However, the impact extended far beyond physical changes. The young men became intensely preoccupied with food—meals dominated their thoughts, conversations, and even their dreams and daydreams. Their interest in food grew so strong that some developed new hobbies, like collecting recipes and reading cookbooks, and a few even shifted careers, becoming chefs.
During the rehabilitation phase, when the men were allowed to eat normally again, many began overeating, which led to issues like headaches and digestive upset. Some even developed binge eating tendencies and exhibited purging behaviors. Even five months into the refeeding process, these disordered behaviors around food persisted.
By the end of the study, the men’s basal metabolic rate (BMR)—the amount of energy needed at rest—had decreased by 40%, as had their muscle mass.
Sluggish Metabolism
Allison Arnet, Family Nurse practitioner, bariatric nurse and Advanced Practice Provider in Obesity Medicine, told the Epoch Times that the TV series The Biggest Loser is a good example of this phenomenon.
“Contestants were highly restricted in their food consumption and were aggressively working out. When they returned to their pre-show lives they regained weight fairly rapidly due to the substantial impact the aggressive change in diet had on their metabolism,” she said.
“Short periods of fasting appear to be good for metabolic health but long periods of not eating enough can damage the metabolic system and cause significant issues with maintaining a healthy lifestyle,” Arnet added.
After weight and fat mass are lost, the body attempts to maintain a lower energy expenditure. This results in a slower heart rate, reduced body temperature, and a sluggish metabolism, while preserving triglycerides to support essential biological functions. This response acts as an evolutionary defense mechanism, designed to protect the body during times of food scarcity.
“When we don’t get enough food, our bodies adapt by reducing energy use for non-essential functions, such as reproduction. This helps us conserve energy for the most vital processes needed for survival, Theresa Gentile, registered Dietician Nutritionist and spokesperson for the Academy of Nutrition and Dietetics recommended, explained to The Epoch Times.
When metabolism slows down, weight regain is likely to occur. Moreover, even when the weight is regained, the metabolic rate often doesn’t fully recover. This phenomenon, known as metabolic adaptation, can persist for up to nine years after the intervention. In contrast, no metabolic adaptation occurs in someone who hasn’t undergone calorie restriction, meaning that those who don’t diet may be in a better metabolic position compared to those who have.
Metabolic Hormones
Metabolic hormones also contribute to weight regain after calorie restriction, as they influence hunger and satiety. When fat is lost, levels of leptin—the hormone responsible for signaling satiety—decrease. This means that the lower your fat reserves, the fewer signals are sent to the brain to indicate fullness. With reduced leptin levels, feelings of satiety diminish, leading to increased hunger and greater energy intake.
It has been shown that even a year after calorie restriction, appetite-stimulating hormones remain affected. This includes ghrelin, known as the hunger hormone, as well as leptin, insulin, and peptide YY, all of which play key roles in regulating satiety and energy balance.
After a period of calorie restriction, the body tends to prioritize fat deposition as soon as food becomes available again, anticipating potential future deprivation.
Therefore, reducing calories may have a limited short-term impact because the body’s mechanisms for maintaining weight are often overlooked in initial recommendations.
While excessive calorie intake may have contributed to weight gain for some individuals, simply reducing calories may not be the primary solution. It might seem counterintuitive, but adequate calories and nutrients are essential for achieving sustainable and healthy weight loss.
Starvation Causes Stress and Mental Health Issues
Insufficient food availability can trigger a stress response in the body, leading to an increase in stress hormones like cortisol, which promotes the storage of visceral fat. Additionally, stress often heightens cravings for calorie-dense, quick-energy foods, making weight loss even more challenging.
Prolonged calorie restriction can lead to negative effects on mood, increasing the risk of depression and anxiety. Cognitive function may also be impaired due to reduced glucose availability for the brain, Mary Curristin, nutritionist at ART Health Solutions, told The Epoch Times.
“If calorie restriction leads to inadequate intake of essential nutrients like B vitamins, omega-3 fatty acids, iron, and other brain-supportive nutrients, cognitive function can decline. Deficiencies in these nutrients are linked to impaired concentration, poor memory, and mood disorders like depression”, Gentile said.
Signs that you’re not eating enough
Gentile noted that the following could be additional signs that you are not eating enough:
- Constant fatigue and low energy
- Constant hunger and preoccupation with food
- Worsened sleep quality
- Decreased strength
- Cold sensitivity
- Disrupted menstrual cycle
- Brittle, dry nails and hair
- New mood swings
- Sudden injuries
How To Resist Weight Regain
Increasing or maintaining physical activity after weight loss is one of the most effective strategies to counteract metabolic adaptations. Regular exercise can enhance fat burning and improve protein balance.
Another effective approach is to focus on the types of foods consumed rather than solely reducing calories. For example, examining macronutrient composition or glycemic load can be beneficial.
High-protein diets can increase feelings of satiety, and more energy is required to metabolize protein compared to carbohydrates and fats. Therefore, increasing protein intake may support long-term weight loss without slowing down metabolism. Research shows that following a high-protein diet can result in less weight regain after dieting. The same benefits apply to a low-glycemic-load diet.
“The goal for weight loss is to create a slight caloric deficit, but not so much that your body enters starvation mode,” Gentile advised.
“Prioritize nutrient-dense foods and incorporate strength training to help maintain muscle mass,” Gentile added.
A version of this article has been published by The Epoch Times.