Is it safe to fast all day and then eat whatever you want at night?
As a general rule, fasting all day on a regular basis is not a good idea, even if you "make up" the skipped calories at night. Although our bodies are remarkable in their ability to adapt to over and under eating at times, they need energy throughout the day to perform at an optimal level.
Paying attention to hunger signals (they are there for a reason!) and being aware of how much food you need to maintain physical and mental energy is healthy. By fasting all day you deny your body nutrients and energy which may lead to headaches, mood swings, feeling tired and dizzy, and even fainting. Your metabolism may also slow down and you could lose muscle mass. Fasting also may make you more likely to binge in the evenings, and you may be more likely to choose unhealthy foods.
You may want to ask yourself why you are skipping meals during the day. Observing religious holidays or special occasions is one reason many people fast from time to time. For most people, our bodies can adapt and function through the occasional fast, whether it is a sun-up to sun-down fast, or extends for a full day (children and people with certain medical conditions may need to forgo even occasional fasting; consult your health care provider if you are uncertain).
If you fast frequently you may want to consider some of your motivations. Are you trying to lose weight? Do you not feel hungry during the day? Are you too busy to eat? If you are trying to lose weight, eating several small meals throughout the day might be a better option. This will provide you with a more constant and consistent source of energy in a form that makes it easier for your body to metabolize and burn calories. Skipping meals is not a healthy approach to weight loss since fasting slows down metabolism and makes people more likely to overeat later. See Will skipping breakfast and lunch lead to weight loss? and Importance of eating breakfast for more information on skipping meals.
You mention eating "whatever you want" at night. Could this be because you feel guilty about eating certain kinds of foods, or about the amount of food you eat? These concerns are issues to think about before you can adopt a more healthful eating plan and positive attitudes toward eating. They may also be a sign of disordered eating, or other issues such as depression. If you're experiencing guilt or are anxious about food, contact a mental health professional who can help you get to the bottom of these feelings and behaviors.
If your question is motivated by the desire to lose or manage your weight, consider making an appointment with a nutritionist or registered dietician who can help you figure out a meal plan that works for you and fits your lifestyle.
Although it's not always easy to change your eating habits, taking care of your health is worth it in the long run.Alice!