Many people believe that exercise is something only overweight people should do, and a lot of people exercise with the sole goal of losing weight. So why should thin people exercise if they are already at the ideal dress size and optimal weight?
Even though exercise helps a great deal with weight loss, it also improves our health in many other ways such as reducing the risk of heart disease, lowering cholesterol levels and reducing high blood pressure. Even though these conditions are associated with obesity health risks, thin and sedentary people shouldn’t assume they are risk-free. Lean exercisers have good levels of LDL cholesterol, the heart clogging variety, as you’d expect. However their thin but inactive counterparts were found to have the same levels of LDL seen in obese people! In fact, an overweight exerciser is actually more likely to be comparable to a thin exerciser rather than an inactive thin person in terms of cholesterol levels. Having high cholesterol and a risk of heart disease is more about how much exercise you get, rather than the your body mass index stat. A study  found that lean exercisers were fitter and had a reduced chance of developing cardiovascular diseases compared to those who don’t exercise.
Exercise is essential for a healthy heart – no matter your weight. Exercise is also helps protect against viruses and disease. In the short term, regular cardiovascular activity can help to boost the immune system, and in turn makes you less susceptible to viruses such as the common cold, influenza and helps to protect against any kind of infection. In the long term, regular exercise makes the body overall healthier, by lowering the risk of serious diseases such as strokes, heart disease, high blood pressure and cholesterol, diabetes and even cancer.
Being thin and being healthy and strong are not a given. Just as there are overweight people who are in good health (the type who exercise), there are many thin people who are far from healthy. Those who work out can run and walk faster and longer distances, and on the whole, have greater endurance.
Exercise is also a great energy boost. It can help to burn away fatigue and raise energy levels. People who work out more often find they sleep better and are more refreshed during the day. If you’re suffering from mental disorders such as depression or anxiety, exercising allows you to disconnect and alleviate stress and relax the mind. Endorphins are released after exercise, which are helpful in battling depression.
Finally, physical activity does keep the pounds off. Most thin people who are sedentary have a fast metabolism, and in some cases this is for life, but for many of us as we age, our metabolisms will slow down and we will inevitably gain weight. So it’s in everyone’s best interest to get in the habit of working out!
 O’Donovan G, Owen A, Kearney EM, Jones DW, Nevill AM, Woolf-May K, Bird SR., Int J Obes (Lond). 2005 Sep;29(9):1063-9.
 http://news.bbc.co.uk/1/hi/health/4778274.stm Accessed October 2011
 http://www.fitday.com/fitness-articles/nutrition/vitamins-minerals/5-reasons-why-thin-people-have-to-exercise-too.html Accessed October 2011