Without getting hooked up to a machine that measures your energy expenditure, working out how much you need to eat per day is a bit of a guessing game.
Your Basal Metabolic Rate (BMR), If you don’t know it you can find out on the internet by filling in your gender, age and weight, is a good starting point for drawing up predictive equations.
How to fuel the Ironman
What to eat during the week before your triathlon
The next step is to work out your ‘activity factor’, which considers both your recreational and occupational activity. As you train 10-12hrs a week, your recreational activity will be ‘very active’. If you do a desk-based job, your occupational activity will be ‘light’, giving you an overall activity factor of 1.6. If your occupational activity is ‘moderate’, your overall activity factor will be 1.8 (1.7 for females), and if your occupational activity is ‘heavy’, your overall activity factor will be 1.9 (1.7 for females).
Once you’ve calculated your overall activity factor, you simply multiply it by your BMR. So, if your occupational activity is ‘light’, your total energy expenditure will be 1.6 x 1,850 = 2,960kcals/day.
Every athlete’s metabolism is different, however, so I believe that listening to your body and eating intuitively based on what’s sensible for that particular day is a great way to go about things.
For example, on heavy training days you need to ensure that you’re eating enough good-quality carbohydrates and fats, to help you get the most from your sessions. If you feel that you’re running low on energy, make a note to increase the amount you’re consuming. Or if you’re feeling heavy and lethargic, you might need to reduce the amount. Similarly, you’ll need to play around with the timing of your intake, as this can greatly help or hinder your training.
Training for 10-12hrs per week is going to increase your appetite considerably, which could lead to over-eating. The best solution here is to ensure that you get in some good-quality carbs post-exercise. Include a good source of fibre (such as wholegrains, skin-on sweet potato or vegetables), and a decent portion of protein (preferably 20-30g of dairy, meat, fish, eggs, tofu or Quorn). Together, these will help you to feel satisfied after a day’s training, and will also supply you with the nutrients you need to aid your recovery.
Best of luck with the training and fuelling.
Sophie Heath is a registered nutritionist with a masters in sport and exercise nutrition