Taking extra fat during long distance running or cycling races will not help you to go faster or win the race. When you exercise intensely, your muscles burn mostly sugar and the more intensely you race, the greater the percentage of sugar that your muscles use.
Researchers in Australia gave nicotinic acid (which prevents muscles from using fat for energy) to male competitive half-marathon runners and then had them run on a treadmill until they were exhausted, at a pace equal to 95 percent of their best half-marathon time (Journal of Applied Physiology, Jan 15, 2016;120(2):107-13). The runners ate meals free of absorbable carbohydrates before and during the run. The researchers set up a situation in which the runners ran as fast and far as they could. They had to stop when they were exhausted from using up all of the stored sugar in their bodies. The researchers found that blocking the body's use of fat:
• did not shorten the distance the runners covered before becoming exhausted, and
• did not increase the rate that their muscles used up the body's store of carbohydrates.
When the runners ran as fast as they could for more than 10 miles, carbohydrates contributed 83 to 91 percent of the total energy their muscles used. This shows that:
• When you exercise as hard as you can for a long distance, you will exercise faster and longer when you load your muscles with as much sugar as possible beforehand and take a sugar source during your event.
• You will not race faster by taking fat during a competition or by getting fatter before the competition. Furthermore, any extra body fat weight will just slow you down.
• These rules hold even if a racer does not load his muscles with sugar before a race and he does not take additional sugar during a race.
• These rules apply to recreational athletes as well as to Olympic champions.
The Science Behind the Research
Muscles use carbohydrates and fat (and a very small amount of protein) stored in the body as fuel during exercise. You have enough fat stored in your body to keep you moving for days. However, you will start to run out of stored sugar in your body when you exercise all-out for more than 70 minutes. The more intensely you exercise, the greater the percentage of sugar that your muscles use for energy. When you are moving slowly, your muscles get almost all of their energy from fat. When you exercise as hard as you can, your muscles get almost 100 percent of their energy from sugar.
How Much Carbohydrate (Sugar) Do You Need?
You need to take in extra carbohydrates to compete at your best in events lasting longer than 70 minutes (Sports Med, 2013 Nov;43(11):1139-55). The very best world-class athletes, who can store the most sugar in their bodies, still need to take in sugar when they compete in events lasting longer than two hours. For prolonged exercise lasting two to three hours, athletes are advised to ingest carbohydrates at a rate of 60 grams per hour (1.0 to 1.1 g/min) and the more sugar that their muscles can use, the faster they will go. Well-trained endurance athletes competing longer than 2.5 hours can use up sugar at 90 grams per hour, provided that they are taking in that much sugar.
You can race faster in events lasting 45 to 60 minutes by taking in extra sugar during your race, even though you have not used up all of the sugar stored in your body. Taking sugar during competition also improves strength, speed and endurance in athletes competing in intermittent-speed team sports such as basketball, football, hockey and soccer (Ned Tijdschr Geneeskd, 2015;159:A7465). Taking carbohydrates immediately after athletes finish a competition hastens recovery, so athletes competing in sports with multiple events within 24 hours should eat a carbohydrate-rich meal as soon as they finish their first competition (Sports Medicine, 2003;33(2):117-144).
Which Sugars are Best for Competition?
The limiting factor to how fast you can move during a race is the amount of oxygen that you can take in and use. Since sugar requires less oxygen than fat to power your muscles, you want to get as much sugar into your muscles as quickly as possible. Anything that increases the amount of sugar that can be absorbed from your intestines into your bloodstream will help you ride or run faster and longer.
Sugars are carried across your intestinal tract into your bloodstream and then into your muscles by special protein transporter molecules (Sports Sci, 2011;29 Suppl 1:S17-27). Glucose has its own specific transporter protein and so does another sugar, fructose. Your muscles can have 75 percent more sugar available when you take in both glucose and fructose, compared to taking in only glucose, because both types of transporter proteins can be used at the same time. When you take in drinks that contain only glucose, you can absorb and use only one gram of sugar per minute, compared to 1.75 grams per minute when you take a drink that contains both glucose and fructose (Current Opinion in Clinical Nutrition and Metabolic Care, July 2010).
Caffeine Increases Sugar Absorption
Adding caffeine to a drink can increase absorption of sugar into the bloodstream by as much as 26 percent (Journal of Applied Physiology, June 2006). Therefore, the most effective drinks for endurance competition may be those that contain glucose, fructose and caffeine, such as are found in many carbonated drinks, sugared coffee or fruit juice plus coffee. These drinks are safe during exercise because contracting muscles can prevent a high rise in blood sugar levels by drawing sugar from the bloodstream without needing insulin. However, when you are not exercising, sugared drinks can cause very high rises in blood sugar, increasing risk for obesity, diabetes and heart attacks.