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How do I lose weight but not compromise training?

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Article written by Nigel Mitchell

Date published 04 November 2021

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Weight management is always one topic that competitive endurance athletes love to discuss. The main issue is: how do you reduce your intake enough to lose weight, but ensure you have enough energy for training?

In endurance sport, carrying extra weight slows you down. On the bike, when climbing on a 6% climb, 1kg is equivalent to having to produce about an extra 6 watts. On the flat, this is reduced.

To understand this we need to examine and challenge some basic principles of nutrition. In very simple terms, the body stores all extra energy in the form of adipose (fat). We store a small amount of energy in carbohydrate; this would be in the region of 60g in the liver and a few hundred grams in lean tissue.

Even in a lean person, the body likes to store about 10kg of fat, and the reason we store all this excess energy as fat is because, weight for weight, fat yields the most energy. 1g of carbohydrate provides 3.75kcal, and 1g of fat provides approximately 9kcal. Body fat (adipose) is not pure fat, so 1g of adipose is approximately 7kcal.

That means 1kg of adipose is worth about 7,000 kcal. Therefore, to lose 1kg of body fat, you need to be in an energy deficit of 7,000 kcal. In exercise terms that is equivalent to someone running about 70 miles, or in food terms this is equivalent to about 28 Big Macs or about 6.5kg of cooked quinoa.

When we train, especially hard training, we use more carbohydrates, and if we do not have the necessary carbs, it will affect the quality of training. We have all under-fuelled and felt the results of 'bonking'.

Lose fat, not muscle

One other point we must consider is that when we are losing weight, we want to lose fat and not muscle. However, all too often when we reduce energy intake, we lose both fat and muscle. A major reason for this is that when we reduce energy, especially from carbohydrate, the body will use more protein. There are both dietary and exercise strategies that can reduce and prevent the muscle loss.

Before starting a weight-loss plan, people should consider whether it is worth the additional work and stress. Also, how much weight have you got to lose? Today there are many body composition monitoring devices, such as scales that use bio-impedance to gauge body composition. The precision of these can be variable, but they can provide a guide for weight loss and the monitoring of that weight loss.

Two people bending knees before lifting barbells in gym

Some weight training will help reduce muscle loss while trying to lose weight.

The key points to consider for effective weight management:

  • How much is the desired weight loss?
  • Following a weight-reducing diet can add additional stress to the body. Only start this if you are in good health.
  • It's a good idea to have iron stores checked, and if low, consider an iron supplement.
  • Plan gradual weight loss. This will compromise training and recovery less than rapid weight loss. 500g-1kg a week is about the maximum you should aim for; this is a deficit of 500-1,000 kcal per day.
  • Try to plan the weight loss at times when you do not have intense training.
  • Ensure that you ingest about 1.5g-2g of protein per kg of body weight a day, split between your meals. For example, a 70kg triathlete would require about 100g-140g of protein a day. Dairy protein is particularly good, but it's not really a problem for vegetarians or vegans: you just have to plan the vegetable protein carefully. Foods such as quinoa, soya, pulses and nuts are particularly good vegetarian proteins.
  • Periodise your carbohydrate intake. If you are doing light or low-intensity training, reduce the carbohydrate around the training session. If the following day you have a hard session, then carbohydrate should be increased after training.
  • Quick and slow carbohydrates. Base your carbohydrates mainly on low glycaemic index (GI) foods such as porridge, sweet potatoes, and quinoa. These carbohydrates are more slowly absorbed.
  • Snacking. Include a mid-morning and mid-afternoon snack. I find something like a banana or about 40g of pistachio nuts works well.
  • Healthy fats. A common mistake is for people to cut fat back too far. Like proteins, we have essential fats as well. I always recommend that when people are on a weight-loss plan that they include fats such as oily fish, eggs, avocado, milled seeds (see seed and berry mix recipe), pistachio nuts and olive oil. I would normally recommend an omega-3 supplement high in Eicosapentaenoic acid (EPA), aiming for 1-2g a day. For elite athletes, I may also include a CLA supplement.
  • Monitor your weight. Try to get weighed on the same scales at the same time each week, and keep a record of this.
  • Resistance work and some strength work will help to reduce muscle loss.
  • For most triathletes, weight management should not be a big issue, and for anyone who is really unsure, they would benefit from some professional dietary input.

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About Nigel Mitchell

Nigel Mitchell is Technical Lead for the English Institute of Sport, nutritionist for British Sailing and an honorary senior lecturer at the University of Portsmouth.