What Are the Main Side Effects of a Low Calorie Diet
Side effects low calorie diet plans can include fatigue, dizziness, nutrient deficiencies, and muscle loss, especially when intake drops below 1,200 calories per day for women or 1,500 for men, according to guidance from the National Institutes of Health. Very low calorie diets of 800 calories or fewer, often used in medical settings, carry higher risks of gallstones, electrolyte imbalances, and slowed metabolism, as noted by the Mayo Clinic. Companies such as Noom and WW offer structured low calorie programs that track intake and side effects through apps, while the U.S. Food and Drug Administration does not approve most low calorie diet products as drugs. The side effects low calorie diet causes vary by individual, with people who have diabetes, eating disorders, or chronic conditions facing greater dangers.
Short term side effects of side effects low calorie diet changes often appear within days and include headaches, constipation, bad breath, and irritability, driven by lower carbohydrate and fiber intake. The Centers for Disease Control and Prevention lists rapid weight loss above 3 pounds per week as a warning sign that a low calorie plan may be unsafe, and advises consulting a doctor before starting. Research published in The Lancet Diabetes & Endocrinology shows that calorie restriction can reduce lean body mass and resting metabolic rate, meaning the body burns fewer calories at rest over time.
Who Is Most at Risk from a Low Calorie Diet
Side effects low calorie diet risks are highest for adolescents, older adults, pregnant or breastfeeding people, and those with a history of disordered eating, per the American Academy of Pediatrics and the Academy of Nutrition and Dietetics. The SEC filings of weight loss companies such as WW International and Nutrisystem highlight these groups as having higher rates of adverse outcomes on very low calorie plans. Data from the National Health and Nutrition Examination Survey show that women aged 20 to 39 are the most likely to try low calorie diets, yet they also report the highest rates of side effects such as hair thinning and menstrual irregularity. People taking medications for blood pressure, blood thinners, or insulin must monitor side effects low calorie diet changes closely, because rapid weight loss can alter drug effectiveness and require dosage adjustments.
Individuals with a body mass index below 18.5, or those who are underweight, face serious side effects from further calorie restriction, including bone density loss and weakened immune function, according to the World Health Organization. The side effects low calorie diet causes in these groups often include hormonal disruptions, with studies in The Journal of Clinical Endocrinology & Metabolism linking severe restriction to lower thyroid hormone levels and increased cortisol. Companies like Noom and Calibrate position themselves as medically supervised options, but their programs still list side effects such as nausea, fatigue, and nutrient gaps in their terms and user agreements.
How to Reduce Side Effects While Following a Low Calorie Diet
To lower side effects low calorie diet risks, experts recommend gradual calorie reductions of no more than 500 calories per day, aiming for a weight loss of 1 to 2 pounds per week, as endorsed by the CDC and the Academy of Nutrition and Dietetics. Eating protein-rich foods, such as lean meats, fish, eggs, and legumes, helps preserve muscle mass, while fiber from vegetables, fruits, and whole grains reduces constipation and hunger, according to research in The American Journal of Clinical Nutrition. The side effects low calorie diet causes related to micronutrient gaps can be managed by choosing fortified foods or taking a multivitamin, but users should check with a healthcare provider before adding supplements.
Tracking tools from companies like MyFitnessPal and Cronometer allow users to monitor calorie intake and identify nutrient shortfalls that drive side effects such as low energy and poor concentration. The side effects low calorie diet plans produce are often temporary when the diet is balanced, with most people seeing improvements in digestion and mental clarity