Some situations make people gain weight and certainly there are circumstances that might lead to weight loss.Conditions like illness might lead to weight loss because many sick people often lose appetite and do not feed normally.After recovery from the illness people tend to strive for weight gain or desire to regain their physical stature.Low levels of metabolic activity might contribute to low activity of muscle cells and this partly explains low energy regeneration in individuals who have recovered from a recent illness.It is worth to understand that it is much easier to lose weight on purpose than to gain it. But the most scientific proven manner to gain weight actually is through proper nutrition. A proper weight-gain diet is the best approach in any endeavour to gain healthy and lean muscle mass. The first rule for anyone aiming at weight gain is to consume more calories (energy) than one expends. This is because much of the food we eat is broken down into calories (energy) to run the body’s metabolic system. In order to gain weight, one needs to ensure that some nutrients remain in the body system so as to build muscles and create some body reserve storage like Fat to increase on the body mass index. Most people who find it hard to put on weight simply do not eat enough calories. This means all they eat is used to run the body systems and nothing remains for muscle building and storage as fat. People should have regular feeding pattern. The body can only utilize certain amount of nutrients at a specific time. Therefore, eating so much between long periods is less effective for weight gain because the body will only utilize a certain amount and pass on the rest. Yet with the aim of building muscles fast, there is need for maximum retention of the nutrients necessary to accomplish body requirements. For example, you can eat four to five small meals a day, each meal coming after about four hours so that the stomach has time to digest each meal fully. This enables the body system to constantly create space for digestion, absorption and assimilation of body nutrients by adding nutrients to its mass from the constant food intake and thereby causing fast weight gain. However, people should avoid inconsistency in the dietary habits while seeking weight gain. The body system works in a manner that it is not able to store fats with insufficient nutrients in the body or when it is unsure whether it will get its next feeding or not. Therefore in an effort to maintain its working mechanisms, the available fat is turned into calories to run the systems when no meals are taken. Yet when the body gets used to being fed consistently, it is less likely to store energy as unsightly fat, rather using it for body building. Our body system relies on a wide variety of nutrients to attain mass. Carbohydrates should be eaten as energy-giving foods for the body’s metabolism. Their calories do not directly build muscles or add to body fat, and so they have to work together with proteins and fats for weight gain.  Foods that are recommended for carbohydrates include whole cereals (like rice), whole grain foods like bread, posho and millet, potatoes, fruits and vegetables. Proteins are the body’s primary raw-material for muscle repair and construction. Without enough in-take of them, consumption of other nutrients will have limited impact on muscle development. Proteins make muscles develop in a lean and proportional shape, as opposed to fats alone which just generate any-shaped mass.  Healthy protein sources include poultry, fish, legumes, nuts and seeds. Red meat is good if eaten once or twice each week, caution should be taken as more red meat contains a lot of saturated fat. Fats and oils not only combine with carbohydrates to provide energy for the body, they also have more than twice the amount of calories provided by protein and carbohydrates. They also play great roles in building muscles that makes them to provide the starting point for manufacture of the body fatty acids that our body needs to support lean muscle growth. Healthy sources of fats and oils include fish, flax seeds, olive oil and nuts. Vitamins boost our body immunity and are therefore necessary to keep us healthy so that any gained weight is not quickly lost to sickness. They also complement carbohydrates and proteins in both muscle-building and calorie provision to our body system.