We have evaluated the nutritional content of food intake (kilocalories, proteins, carbohydrates, lipids, vitamins and minerals) before and after a low caloric diet in a sample of 25 overweight and obese patients. We have also measured several biochemical parameters such as glucose, magnesium, iron, calcium, total cholesterol, high-density lipoprotein (HDL) cholesterol and thyroid stimulating hormone (TSH). We have found an imbalanced intake of vitamins and minerals during the low calorie diet in all of the patients included in the study. In order to assure the Daily Recommended Intake of vitamins and minerals we need to be more careful regarding both food quantity and quality during a nutritional intervention. Medical professionals should also promote the vitamins and minerals as dietary supplements in patients undergoing a low calorie program.