There has been a lot of informal debate over whether eating one meal per day is a good weight loss and weight maintenance strategy. The available research indicates that a one-meal strategy is not the best way to lose weight or maintain a desired weight, and it may have some negative effects.

Eating only once a day will not allow you to eat the amount of kilocalorie (kcal) your body needs. You may manage 500-600 kcal in one meal and for somebody who needs around 2,000 kcal a day this amount is very little. You are not getting enough protein, fat, carbohydrates, nutrients, enzymes etc. Without these components your body doesn't have anything to build from. So, reproducing new cell and keeping up body the functions become very hard. Slowly your body will degenerate and the consequences are many.

Proteins serve the body as building blocks in the growth and repair of tissues. Even to build up muscles you need protein. As your body can't store excess protein, you need it regularly in small amount throughout the day. It means that by eating a big stake in the evening you might be getting a lot of protein but as you are getting it in only one meal your body can only use part of it. Women can use approximately 20g of protein after a meal. One needs minimum 60-80g of protein a day, and more if one is training. When one doesn't get enough protein with the diet one's body will use the protein one has in one's muscles to keep up body functions. This will lead to degeneration of the muscles.

Eating too little will affect your immune system. Obviously you are not getting enough nutrients to fight diseases around you. And this is the most dangerous side effect of under-eating.

By eating infrequently you slow down your metabolic rate. Your BMR indicates how many kcal your body burns a day. When you eat less than you need, your body goes into starving mode, the BMR slows down and you burn much less kcal than you should be doing. This is a defence mechanism that is crucial for your survival. If you eat 600 kcal and your body keeps burning 2000 you will die, as simple as that. Now whenever you eat more you will put it on, meaning that you are now prone to put on fat.
When people go on a strict diet, it affects their metabolic rate in a negative way, when they start eating normally again they put on weight because their body is now burning less than it used to. They go again on a diet and the same thing repeats which is the most common reason for why people gradually put on more and more weight.
To burn fat you need energy, it means that if you are trying to get cut, get rid of the excess fat on your body you need first to provide your body with energy. When your body doesn't have enough energy, it doesn't burn fat effectively. It burns protein (your muscles).
Eating frequently is actually proved to be the most effective way to burn fat and it also allows you to burn the maximum amount of kcal your body can burn. It has to do with controlling your insulin level along with other
hormones.
By under-eating or simply by eating seldom you are affecting your energy level. Your energy level will determine how well you perform at work, in the gym and it also affects your brain function. So, low energy level doesn't allow you to use your brain effectively. When you start eating properly and frequently, you will feel the difference.
Under-eating affects your mood. Your body and mind are directly linked together. Whatever is happening in your body will affect your mind. Under-eating usually makes you irritated, depressed and in general unhappy.

What to eat when Breakfast
Breakfast should be based on carbohydrates as this is when you need energy to kick start the metabolic rate.
Morning
Morning should also be mainly based on carbohydrates as your body is still in need of energy. Either the morning or the breakfast meal should include some protein as you need the protein in small amount throughout the day.
Lunch
Lunch should be equally based on carbohydrates and protein. It is also essential to include vegetables in this meal. Salad is not enough.
Afternoon snack
Protein based meal is more appropriate as your body's metabolic rate is now slowing down and your need for energy is diminishing.
Dinner
More protein and vegetable based meal. You need protein at this time as it is during the night your body is rebuilding itself.
Eating only one meal a day can harm your health. Eat enough and frequently. Enjoy good health and stay active.