Marathon Runner or Triathlete

  • Lasting more than 90 minutes

In marathon running, the main energy source is almost exclusively aerobic metabolism of fat (98% to 99%). Only a small amount of energy comes from anaerobic metabolism of carbohydrates (1% to 2 %). The aerobic metabolism of fat also requires adequate glucose for maximum efficiency. Therefore, marathon runners need slightly more fat and slightly less carbohydrate than middle distance runners.

I would recommend a diet where: 

  • 55% of calories come from carbohydrates
  • 15% of calories come from protein
  • 30% of calories come from fat

In this case, the ratio of grams of carbohydrate to protein is 3.7:1 and the ratio of grams of fat to protein of 1: 1.

As an example, a 73 kilogram (160 lb) male marathon runner whose basic metabolic requirements are 3200 calories per day, would have to consume 377 grams of carbohydrate, 102 grams of protein, and 102 grams of fat per day just for the energy they need to go about their daily activities.

Then add to this the number of calories burned per day in training and competition, with protein, carbohydrate and fat divided out in the same ratios, to get their total requirements for the day.

In spite of the small percentage of their energy that comes from anaerobic metabolism of carbohydrates, marathon runners run the risk of depleting their glycogen stores due to the long duration of their training sessions and competitions.

Since the brain needs sugar as a source of energy, depleting your glycogen stores will cause you to become hypoglycemic and your brain will become foggy. Marathon runners in this condition have been known to lose their sense of direction and eventually pass out. For this reason you must carb load while tapering your training during the seven days before a competition, and ingest carbohydrates during the long training sessions and competitions.


According to Tim Wierman (Nutrition for Swimmers: Eat to Win) the average swimmer ‘s diet consists of 46% carbohydrates, 38% fat, and 16% protein, which is too little carbohydrate and too much fat. This inadequate intake of carbohydrates will leave them short of energy when they compete.

Some young athletes will do the opposite and give up all fats because they think they only need carbohydrates. Then they eat more carbohydrates than they need, and since any calories not utilized by the body are converted to fat and stored, they gain weight.

You can look up the “Nutrition Facts” label for any food (even the ones that don’t come with a nutrition label such as oranges or bananas) at, which you can access Here.

“Maintenance Number” Definition

The “Maintenance Number” is the number of calories an athlete needs to maintain their energy level throughout the day.

  • For males – it is body weight (in pounds) times 15 (lb x 15) plus the training.
  • For females – it is body weight (in pounds) times 13 (lb x 13) plus the training.

This will give you a good estimate of the number of calories you need to consume on a daily basis in order to maintain your weight without gaining or losing. The Training needs will depend on the sport in which you compete and even the individual event in your sport.

If you’re a swimmer the number of calories burned per hour depends on which stroke you are doing.

With any sport where you break out into a sweat, you will likely burn 300 to 700 calories per hour, depending on your weight and the level of intensity.

Every athlete should calculate their “Maintenance Number” and ensure that they are consuming adequate calories in order to maintain their present body weight and have enough energy to get through their daily activities and training. There is an excellent “calories burned calculator” at

Access the calculator Here>

“There is also an App for this (for both iPhone and Android). Look for “Health Calcs”on iTunes or at the Google Play Store.

Learn more about Pre-Competition Nutrition Requirements.

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