Whether running in the morning is more effective for burning fat has long been a topic of interest for runners and those seeking to lose weight. Ultimately, there is no hard scientific evidence that conclusively supports this theory, though there are several aspects to early-morning aerobic exercise that should be considered. In the end, everybody reacts differently to what time of day he runs. The best way to find out what works for you is simple trial and error.
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Running Before Breakfast
There is a wide range of theories on whether running in the morning is beneficial. One theory is that running before eating breakfast is an efficient way to burn calories -- because there is no food in the stomach, the body has to rely on fat as an energy source. This theory is only partially correct, however. Your body eventually begins to burn carbohydrates and turns to lean muscle tissue as its primary source for energy. In this case, running on an empty stomach in the morning does not burn significant amounts of fat, and is a counterproductive way of exercising since your body is breaking down lean muscle.
Your body does not perform its various functions with equal efficiency throughout a full day. A cyclic process known as circadian rhythms control your body's performance. Functions such as athletic performance, metabolism and calorie-burning, fluctuate in efficiency over a 24-hour period. One indicator of body functions efficiency is core temperature. The human body performs best when its temperature peaks, which is typically in the mid- to late-afternoon hours, "Running Times" magazine reports. Your body is coldest in the morning hours, which would indicate that running in the morning would not optimize the amount of calories you burn.
Trial and Error
The best way to determine whether running in the morning, either with or without having eaten breakfast, or running at another point in the day optimizes the number of calories you burn, is to simply try out these various times and record your progress. Run in the morning for at least four to six weeks and track your weight loss or gain. Then run during for at least four to six weeks either in the mid- to late afternoon or during evening hours and track your weight loss or gain. Compare the results to see which routine is more effective based on how much weight you've lost, if any. Ensure that you create and stick to a regimented routine and limit any variables that could affect your trials, such as eating snacks or drinking alcohol.
Ultimately, the key to losing weight is to burn more calories than you consume. This principle does not hinge on what time of day you exercise or what time you eat. Cutting calories from your diet, combined with regular exercise, is the most effective way to lose weight. This is a long-term approach to burning calories, which means you must dedicate yourself to a strict diet and exercise plan. Cutting calories for only a couple of weeks won't produce significant results. Ensure that you don't eliminate entire food groups from your diet. Healthy and well-balanced nutrition is still key. Instead, reduce the number of calories you consume from each food group.