With the rise in overweight and obesity, it can be tempting to try new and different diets to find one that works. When an individual is trying to lose weight, there must be an energy deficit, more energy must be burned and fewer calories consumed. A popular method for long term weight loss is a decrease of approximately 500 calories per day, which if followed, results in weight loss of 1 pound each week. Low calorie diets have a greater caloric restriction and can sometimes leave the dieter with uncomfortable and unhealthy signs and symptoms.
Immediate Signs and Symptoms
Low calorie diets provide 800-1200 calories per day, while very low calorie diets provide a minimum of 600 calories per day (ref 1). Diets such as these are done under supervision by doctors and dietitians to ensure that 100 percent of vitamins and minerals, called micronutrients, are consumed. In addition, one must eat enough macronutrients - fat, protein, and carbohydrate - to fuel the body. According to a 2015 article in the British Journal of Obesity, consuming a diet with too few calories can lead to immediate signs and symptoms of deficiency such as fatigue, hair loss, headaches, constipation, muscle cramps, dizziness and cold intolerance (ref 1).
Signs and Symptoms of Micronutrient Deficiency
In low calorie diets, it can be difficult to consume the recommended daily allowance of each vitamin and mineral. Common nutrient deficiencies with low calorie diets are iron, vitamin D, and zinc (ref 2). Those with an iron deficiency may experience unexplained fatigue, pale skin, cold intolerance and decreased immune function. Vitamin D can be difficult to obtain in the diet, so consumption of vitamin D rich foods must be planned in a diet with limited calories. A long term symptom of vitamin D deficiency is muscle weakness. Zinc deficiency might cause impaired healing of wounds or cuts, recurrent sickness, and decreased appetite (ref 3, p 338, 426, 431).
Signs and Symptoms of Macronutrient Deficiency
Macronutrients all have a place in a low calorie diet. Noticing an increase in sickness could indicate protein deficiency (ref 4, p 609). Many low calorie diets decrease the amount of fat, due to the increased amount of calories that fat provides. Not consuming enough fat could lead to deficiencies of vitamins K, E, D and A, as fat is needed for absorption. If those vitamins are not absorbed, signs could be impaired blood clotting - vitamin K, decreased ability to see at night - vitamin A, tiredness and unexplained aches and pains - vitamin D, or pain in hands and feet - vitamin E. Some low calorie diet plans drastically decrease carbohydrate intake. A 2008 study published in the Indian Journal of Psychiatry indicated that diets too low in carbohydrate could cause depression (ref 5).
When to Seek Medical Care
Low calorie diets are an effective means for weight loss, but must be done under close supervision. In some instances, low calorie diets can lead to disordered eating. Adherence to a specified diet plan is essential to ensure that vitamin, mineral and macronutrient deficiencies do not occur. If planning to start a low calorie diet or very low calorie diet, please consult a medical doctor or a registered dietitian to ensure a low calorie diet is appropriate and to assist in meal planning. If experiencing current signs and symptoms from eating too few calories, seek medical care immediately.