Question: I am training for my first Ironman. How do I change my diet to support my increased workout volume?
Answer: The answer to your question depends on how well you have been meeting your needs for calories, carbs, protein and fat thus far in your training. If you have been eating a sufficient amount of protein — meaning you are taking in 1.4–1.6 grammes of protein per kilogramme of body weight per day (roughly 100–115 grammes for a 73kg athlete, or 75–85 grammes for a 55kg athlete)—then you may not need much more protein. You’ll want to dial in your protein intake, as it supports muscle recovery and immune function.
Your body also needs a lot of carbohydrates to support training and recovery. Your carb needs can easily increase from five grammes per kilogramme per day to eight-plus grammes when training jumps from an hour to two or more hours a day (a jump from 350 to 580 grammes of carbs per day for a 73kg athlete, and from 275 to 430 grammes of carbs per day for a 55kg athlete).
Your fat intake should increase to keep up with your jump in calorie needs, to provide anti-inflammatory benefits to counteract the effects of high training volume. Keep your total fat in- take between 20 and 30 per cent of your total calories (a need of 80–100 grammes of fat per day for the 73kg athlete, and 65–80 grammes for the 55kg athlete).
If you want exact calculations based on your individual metabolic rate, training volume and weight goals, seek the advice of a board-certified sports dietitian (C.S.S.D.) who can review your training and food log and make specific recommendations for you.
Athletes should reassess their calorie, carb, protein and fat needs at the start of each season, and with every change in training block, to ensure all of their hard work pays off with maximized energy, optimised body weight and peak performance.