The question often comes up about exercising for long periods of time and achieving little to no weight loss, especially with people who participate in endurance events like ½ or full marathons and triathlons. The logical assumption is that if we exercise for long periods of time that we will “burn” calories and lose excess weight and as most find out, this is not necessarily the case.


The body needs energy to work efficiently while exercising, so for example if a person were 190 lbs with 35% body fat and then progressively reduced their weight to 150 lbs with a 25% body fat (which is a healthy # for females) then the total weight loss is 40 lbs, factor in water and muscle loss and the fat loss total could be approximately 30 lbs. Now the standard measurement of potential energy stored in fat is 3500 calories/lb and the average human usesrunner 2 100 calories to run 1 mile, so all things being equal the potential energy stored should be enough for a person to run just over 1000 miles, so approximately from London to Barcelona or New York to Memphis or about 40 marathons! Now you may or may not know this but most runners tend to ‘hit the wall’ at about 18 – 20 miles, which is when stored muscle energy (glycogen/sugar) depletes yet there is still stored fat energy, the analogy I think is the easiest to understand is it’s like a gas tanker truck sitting on the side of the road having ran out of fuel but the cargo tank is still full.


So why don’t we use the fat?
The body has to be fat adapted as it takes more work and is a slower process for the body to convert stored fats to usable energy and so it needs to be trained to use fat for energy, so if endurance athletes keep using gels and sugars for energy, before, during, and post exercise then their body’s go to fuel is sugar and when it runs low they will stop. The paradox for athletes who want to lose weight is that if they cut back on calories then their performance suffers and if they keep up their energy levels then fat loss is stalled. Fat loss is possible with endurance events but it will be a slower rate, I think it hinges on being smart with calories and eating more around workout days, eating more whole starches like potatoes, rice, squash etc. and avoiding processed ones and also raising the healthy fat content of the diet too to promote fat usage for energy. The majority of fat usage will be the hours post exercise as the body restores muscle glycogen levels and also on rest days when the body can utilize the stored fat at it’s disposal.

Yours in health,

Richard Insley

2016-08-23 13:52:27