Relying solely on calorie intake doesn’t account for the large number of variables that may prevent someone from losing weight even when on a very low-calorie diet. Hormonal imbalances, health conditions like hypothyroidism, metabolic adaptations, the use of certain medication, and genetics are some of the factors that may make weight loss harder for some people, even when they are on a strict diet. 

It is not advised to go on such diets as they create nutritional deficiencies. Having a balanced meal plan with nutritional foods is very important even when trying to lose weight.