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When to eat is as much of a question as what to eat for those in training for a marathon. Here, as part of our Marathon Nutrition Advice series, Jane Nodder explains how to fuel for a marathon before, during and after the race.
Training for a marathon? See our Marathon Training section.
Described by John Ivy and Robert Portman in their 2004 book, ‘nutrient timing’ has become a popular idea in sports nutrition in recent years.
The concept focuses on ‘when’, as opposed to just ‘what’ to eat to optimise performance during training and competition, and promote glycogen replenishment, growth and repair and overall recovery.
This can be crucial for the endurance athlete and a real challenge to the non-elite runner who juggles many commitments.
To illustrate the Nutrient Timing concept, Ivy and Portman referred to three critical phases in the day: the Energy Phase, the Anabolic Phase and the Growth Phase.
The Energy Phase
This phase occurs ten minutes prior to and during training and competition when energy demands by skeletal muscle are at their highest. The focus is on providing nutrients to spare carbohydrate and protein, support the immune system, minimise muscle damage and allow for faster post-exercise recovery.
Carbohydrate intake is really important in this phase for muscle glucose uptake and glycogen replenishment although some studies have shown a benefit for consuming both carbohydrate and protein before, during and after endurance activity.
For example, including a protein/carbohydrate food or supplement just before, or during, exercise can increase blood flow to muscles and provide amino acids and glucose that can help to reduce muscle glycogen depletion and counteract dehydration. Providing additional amino acids and glucose can also reduce levels of the stress hormone cortisol so improving the immune response.
Any food or drink that provides protein and carbohydrate during exercise should be well-diluted and easily digested. Drinks should contain a combination of glucose and maltodextrin with whey protein/hydrolyzed whey protein diluted to a 6-10% solution (i.e. 60-100g of protein powder to a litre of water) in order to replenish water stores appropriately. To target the strength of a drink more individually, start with 0.8g of carbohydrate and 0.4g of protein per kilogram of bodyweight per litre of water.
Always start to take in energy shortly after you start running, as it seems more effective to take on carbohydrates at 15-20 minute intervals during activity, than to take in the same amount of carbohydrate after 2 hours of exercise. Consuming carbohydrate during exercise is particularly important for runners who do not eat before training, or who restrict their energy intake for weight loss.
The Anabolic Phase
Food intake and timing post exercise depend largely on the effects of duration and intensity of the exercise session glycogen levels and on the timing of the next exercise session. Muscle glycogen production can be impaired for several days following extensive training that causes muscle damage e.g. in a marathon, and complete restoration of glycogen stores may take more than 24 hours even with a high carbohydrate intake. The more quickly muscle glycogen stores can be replenished, the faster recovery occurs.
Ivy and Portman use the term ‘Anabolic Phase’ to describe the ‘window of opportunity’ that lasts for approximately 30-45 minutes following exercise when muscles are particularly sensitive to the activity of anabolic hormones such as insulin, testosterone, growth hormone and insulin-like growth factor-1 (IGF-1). These hormones increase the body’s ability to recover by promoting anabolism, muscle blood flow, restoration of glycogen stores, repair and growth of tissue including muscle and supporting the immune system. Including sources of carbohydrate in this phase increases the amount and rate of glycogen storage and muscle repair and growth, whilst combining protein and carbohydrate replenishes muscle glycogen even more rapidly than carbohydrate alone, and creates a more favourable environment for muscle growth.
To maximise muscle glycogen replenishment, try to eat at least 50g of carbohydrate (1.0-1.5g/kg/body weight) and 10–15g of protein with fluid within 30-45 minutes of training or competing in an endurance event (more than 60 minutes). For suitable meals and snacks see the article on Carbohydrate Loading for Runners and Sources of Protein for Runners.
The Growth or ‘Rest Of The Day’ Phase
The ‘Growth Phase’ refers to the ‘remainder of the day after training’ i.e. the period that begins about 45 minutes after your exercise session till about ten minutes before your next session. During this period providing both carbohydrate and adequate protein during the four hour period following exercise supports the processes of glycogen repletion and muscle protein synthesis and growth. However, since insulin sensitivity and muscle protein turnover fall over time, it then becomes important to focus on meals containing smaller amounts of complex carbohydrates (e.g. fruits, vegetables, beans, quinoa, brown rice, oats) and slower digesting proteins (e.g. meats, cottage cheese, yogurt) rather than high glycaemic index carbohydrates and rapidly digested proteins.
Rebound or reactive hypoglycaemia
During the 1970s, a couple of studies indicated that some athletes experience high blood glucose and high insulin levels followed by ‘rebound or reactive hypoglycaemia’ (low blood sugar levels) 15–30 minutes into exercise, if they consumed carbohydrate within 30–60 minutes of starting exercise. This was thought to affect their performance. However, more recent studies have found no effect on performance, or link between blood sugar levels and performance following consumption of carbohydrate before exercise, even where subjects developed hypoglycaemia.
Hypoglycaemia is less likely to occur with larger (75g-200g) amounts of carbohydrate just 15 minutes before exercise and low glycaemic index carbohydrates do not seem to result in hypoglycaemia. Nevertheless, some athletes may develop hypoglycaemia under all conditions, indicating that this response may be specific to individuals.
Applying nutrient timing in practice
You will need to practise your individual strategy for timing your food and fluid intake in relation to the duration and intensity of your training programme, your individual food tolerances, your other commitments and ease of access to your required foods. Make sure you include suitable pre- and post- exercise snacks in your diet to benefit fully from the ‘nutrient timing’ windows. Remember that any meal or snack consumed before exercise should provide fluid to maintain hydration, be relatively low in fat and fibre to support gastric problems, be relatively high in carbohydrate and moderate in protein to support blood sugar. Remember also that we have already considered how you can work out your own personal energy, carbohydrate and protein requirements. See Carbohydrate Loading for Runners and Sources of Protein for Runners. We’ve also considered how to add carbohydrate via sports drinks, gels or solid food in the article Hydration Guidelines for Marathon Runners.
Ideas for pre- and post-exercise snacks combining carbohydrate and protein:
Actions for this week
John Ivy & Robert Portman (2004) Nutrient Timing. Basic Health Publications Inc. Laguna Beach, CA.
John Ivy & Robert Portman (2004) The Performance Zone. Basic Health Publications Inc. North Bergen, NJ.
And if you need more help to build your personal nutrition plan, email Jane Nodder at firstname.lastname@example.org for details of individual nutrition coaching services for runners.
Jane works as a nutrition lecturer and clinic tutor on the MSc and BSc (Hons) Nutritional Therapy programmes at the University of Westminster, London.
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