Start to monitor your personal food and drink intake at this early stage in your marathon training programme.  Over the next four weeks, Jane Nodder of Nutriworks will be considering exactly how you can translate general nutrition and hydration guidelines for marathon runners into food and drink on your plate.

Start by downloading our Marathon Food and Training Diary.

Nutrition and marathon runners 

Preparing for a marathon is an intense endurance activity even if you've been running for a while.  Whilst consistent training helps you adapt physiologically and biochemically to the demands of training, a sound approach to nutrition and hydration is also key in helping you recover well between training sessions and stay injury free (runners' injury advice here) and healthy throughout your training period.  It's also important to protect your longer term health.

However, runners frequently prioritise other training concerns and often only think about nutrition in terms of basic guidelines for healthy eating or the use of supplements.  And whilst it's true that there's no single 'magic' food solution to improving marathon performance, there are some helpful nutrition and hydration guidelines that everyone can adapt for their age, gender, intensity of training and state of overall health. 

Nutrition Guidelines for Marathon Runners - Eating Enough

Compared to the general population, endurance runners generally need more energy and fluid intake to fuel their running, support their blood sugar levels, replenish their glycogen stores, cover their sweat losses, build and repair tissue and maintain their weight.

Marathon running mainly uses the body's 'oxidative system' to produce energy from glucose, protein and long-chain fatty acids.  During the first 1.5-2 hours of running, glycogen (stored glucose) and body fat are the main sources of energy.  After this, body fat alone becomes the primary source.  While trained individuals can use more fat than untrained individuals at the same workload, there must be some glycogen left in the muscles and liver to use the fat efficiently.

Therefore it is important to eat appropriately to encourage muscles to use as little glycogen as possible (glycogen sparing) while stimulating the use of fat as a primary source of energy.

In 2005 a review of seven studies found that the diets of many endurance athletes were low in carbohydrate and high in fat.  In addition, many athletes, particularly females, were probably not eating enough food to meet their energy needs.  Low calorie intake can compromise immune, hormone, metabolic and musculoskeletal function, and increase the risk of fatigue, injury and illness, resulting eventually in difficulties with recovery and poor performance.

Not eating enough also affects micronutrient status particularly for iron, calcium, vitamin B12 and zinc which can fall below the recommended daily allowance (RDA).  And, runners with the lowest energy intake may produce high levels of the stress hormone cortisol.  This can disrupt the reproductive system and have negative effects for bone mineral density, particularly in women.  
 

Carbohydrate Requirements

Carbohydrate is needed to maintain blood glucose levels and replace muscle glycogen after training.  Adequate and regular carbohydrate intake before and during exercise may also minimise the release of hormones such as cortisol.

Guidelines for carbohydrate intake for endurance runners are typically expressed as a percentage contribution to energy intake, with endurance athletes traditionally being advised to get more than 60% of their dietary energy from carbohydrate-rich foods with a moderate to high glycaemic index.

However, using percentages to calculate how much each macronutrient should contribute to total calorie intake may mean that runners eat too much, or too little, of a macronutrient as their total calorie intake increases or decreases.  As a result, it is becoming more common to express requirements as Guideline Daily Amounts (GDA) in grams per kilogram of bodyweight per day (g/kg BW/day).  Using this system, overall recommendations for carbohydrate intake for athletes are: 

Level of Intake             Type of Training    

5-7 g/kg BW/day            General training needs ( Less than 1h low intensity exercise)

7-10 g/kg BW/day          Endurance training (1-3h of moderate to high intensity exercise)

In practical terms, both methods for calculating requirements are challenging for the non-elite athlete trying to translate guidelines for carbohydrate intake into actual ‘food on the plate’.  What figure should they use from the ranges given?  How do they work out the intensity of their training session? How do they meet their energy needs without eating too many simple sugars and ‘grazing’ all day.  

Protein requirements for marathon runners

Guidelines for protein intake for athletes have been debated for many years, with the key question focusing on how much protein is enough?  Despite a scarcity of data regarding actual protein intake amongst athletes, there is evidence both that endurance training increases the need for protein, and that endurance athletes have the same need for protein as the general population.  Other discussions focus on whether protein use becomes more efficient in response to endurance training and whether protein-metabolic responses to exercise differ by gender. 

Despite the ongoing debate, protein intake above the recommended daily allowance is commonly recommended for recovery from intense endurance training, based on the increase in protein use during endurance exercise, and the results of nitrogen balance studies that measure protein use.  Guidelines for daily intake for endurance athletes range from 10-35% of total energy intake, or 1.2 to 1.7g/kg BW/day, compared to 10-15% and 0.8g/kg BW/day for the general population.

If runners increase their protein intake they do still need to consume adequate calories from carbohydrates to maintain body weight and ensure amino acids needed for repair and recovery are not used to meet energy needs instead.

For vegetarian athletes, recommendations for protein intake are 1.3-1.8g/kg BW/day.  However, as plant proteins may be less well digested than animal proteins, runners may need approximately 10% more protein to meet their training needs.  Individuals who avoid all animal proteins (e.g. vegans) may find their diets are limited in certain essential amino acids such as lysine, threonine, tryptophan and/or methionine.

Fat Requirements

Guidelines for fat intake are more complicated than those for carbohydrates and protein!  In general, runners are advised to obtain 25%-30% of their total calorie intake from fats, but this figure is broken down between the different types of dietary fat.  You can download the breakdown of the guidelines here: Daily Fat Intake Guidelines.

Neither high nor low-fat diets appear to benefit endurance performance, and so the most important issue to focus on is including some saturated fat and, most importantly, some essential fatty acids (EFAs) every day to make sure your diet is not 'fat-free'.

EFAs - popularly known as omega 3 and omega 6 fats - are being increasingly studied for their role in supporting athletic performance.  EFAs support all aspects of cell function including fatty acid metabolism and the storage of glucose as glycogen - both vitally important for marathon runners.  EFAs reduce the risk of cell damage that can result in blood loss, support tissue growth and repair and promote the production of anti-inflammatory chemicals.  They may also improve muscle function and recovery under endurance conditions.

We need to obtain the parent omega 3 and omega 6 EFAs from our daily diet as they cannot be made in the body.  Runners who do not eat eggs or oily fish may need to pay particular attention to including daily sources of the omega-3 fatty acid docosahexanoic acid (DHA) in their diet. 

 

Approaches to hydration

What to drink is probably one of the most common topics of discussion for non-elite runners during marathon training periods with both experienced and less experienced runners finding it difficult to translate general guidelines into personal fluid requirements to plan an appropriate hydration strategy.  

In the body, hydration levels are controlled by the rate of water intake in relation to the rate of water loss.  On average, marathon runners can lose 1.0-2.5 litres of sweat per hour and 2-10% of body weight depending on training and race conditions.  Women may lose a greater proportion of body water and plasma volume, despite sweating less in the same conditions, although smaller athletes may sweat less due to a reduced body surface.  

For endurance runners, the main goal of a hydration strategy is to prevent excessive dehydration, and reduce the risk of compromising performance, particularly in hot weather.  Recent research suggests that a level of dehydration for sustained periods may not pose a serious health risk and that it may not be necessary, or even advisable, to replace all fluid lost in sweat.  However, such controversy makes it even more important to work out and practise an individualised hydration strategy. 

Water is perhaps the most important, and possibly the most overlooked nutrient, for muscles and cells to function as effectively and efficiently as possible both in training and in competition.  The main sources of water for humans are liquids (two-thirds of daily intake), food (one-third of daily intake), metabolic water i.e. water produced in the body as a result of energy production (about 280ml per day) and glycogen-bound water i.e. water stored in muscles along with glycogen (about 85ml for every 28g of glycogen).  

Micronutrients

Marathon training increases the demand for micronutrients such as vitamins and minerals.  Although runners can generally meet their additional needs through higher calorie intake, this does depend on the quality and variety of food and drink that individuals consume.  Low levels of micronutrients such as vitamins C, D, E and folate, and the minerals magnesium, calcium and iron can be of real concern in runners' diets.  

What do these guidelines mean to me?

Over the coming weeks we'll consider exactly how you can translate the guidelines set out above into 'food and drink on your plate'.  Next week we'll look at building and tracking your personal nutrition plan.  After that we'll focus in turn on each of the three main macronutrients - carbohydrates, protein and fats - what, when and how much to eat and which sources to choose.  We'll also look at easy meals to add to your nutrition plan.

What can I do this week?

To make best use of the information that's coming up in the next month, it's a good idea to start monitoring your personal food and drink intake as your marathon training gets underway.  You can do this with a Food & Training Diary that you can record in any format e.g. in a spreadsheet or Word document, on your phone or in a notebook.  It's important to record all food, fluids, supplements and supplemental foods that you consume each day using household portion sizes. It's also helpful to note the training you complete and how you feel during your training session and throughout the day.

If you would like an example of a format for recording this information, download our Food and Training Diary here. 

Step 3 of the Marathon Nutrition Guide will be available on therunningbug.co.uk Monday January 2012 for the next article in the series 'Putting it all together - building and tracking your nutrition plan'.
About Jane Nodder

Jane works as a nutrition lecturer and clinic tutor on the MSc and BSc (Hons) Nutritional Therapy programmes at the University of Westminster, London. 

For more information about running and nutrition coaching services from Nutriworks, including details of an introductory seminar 'Nutrition for Marathon Runners' on 21 January 2012, visit www.nutriworks.co.uk or contact Jane directly on 07850 705848 or email info@nutriworks.co.uk. 

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