Does ‘carb loading’ really work?

This is something that was flagged up in a recent nutrition talk by Javier Gonzalez (Northumbria University) at a local athletics club. It was mentioned again on twitter recently as a question, so I thought I would look into it.

What is carb loading exactly?

‘Muscle glycogen levels are normally in the range of 100-120 mmol/kg ww (wet weight).  Carbohydrate loading enables muscle glycogen levels to be increased to around 150-200 mmol/kg ww.  This extra supply of carbohydrate has been demonstrated to improve endurance exercise by allowing athletes to exercise at their optimal pace for a longer time.  It is estimated that carbohydrate loading can improve performance over a set distance by 2-3%’. Australian Institute of sport
This does not mean eat loads on the days leading up to a long distance event!! Carb loading is reported to be one of the most misunderstood concepts in sport.  Peterson says that with these increased energy stores, the competitor will be able to avoid exercise-induced hypoglycemia and continue exercising longer than if this saturation process had not occurred. I have found reference to that fact that this is in fact how carb loading works, in more that one location.

Who should consider carb loading?

Anyone training or competing at distances that are longer than 90 minutes in duration, so this could include longer distance triathlon, marathon running, endurance sports, long distance swimming, cross country skiing, and so on. It seems that with any shorter training, the body’s carb stores are sufficient to cope. It also seems that females may be less responsive because they struggle to process higher carb loads due to disruptions with the menstrual cycle. There has been little research on this matter so far, and most research is based on men.

‘It can be predicted that even with full glycogen stores, a less conditioned athlete’s liver will be depleted of its carbohydrate within and hour and three quarters of continuous moderate intensity exercise.’ David Peterson

How do I know carb loading will work?

A low GI (high carb meal) before running has been proved to improve performance in men here: http://www.ncbi.nlm.nih.gov/pubmed/17240783

This research suggests that carb loading does in fact work and relates the improvement again to preventing exercise-induced Hypoglycemia http://www.nutritionjrnl.com/article/S0899-9007(04)00116-9/abstract

It is suggested here that carb loading can improve performance by up to 20% in endurance sports, if done correctly. If you search the term and follow the links within this document you will find many many more references to suggest that carb loading does in fact work.

How do I go about Carb Loading

Some research has been done in the past, by Texas and Ohio State Universities where they have formulated a plan on how to Carb load.

‘It's easy to figure out how to carbo-load using the Ohio State pattern. Simply multiply your weight in pounds by three. Divide the result by 16 to determine the number of grams of carbohydrate to eat every 15 minutes. Example: Penny weighs 117 pounds. 117 X 3 = 351. 351/16 = 22. 22 grams of carbohydrate should be ingested every 15 minutes.

Since you usually don't think about how many grams of carbohydrate you're actually ingesting, we've made things easier for you by listing food servings which provide about 20-25 grams of carbohydrate:

(1) Two cups of skim milk

(2) A little more than half a bagel

(3) A two-thirds cup serving of cooked pasta

(4) An apple or a banana or a pear

(5) Four dates

(6) A cup of orange juice

(7) One-fifth of a cup of raisins (or two half-ounce packets)

(8) An ounce and one-half of corn chips

(9) A medium baked potato

(10) A slice and a quarter of most breads

(11) Two slices of non-fat 'diet' bread

(12) A cupcake

(13) An English muffin

(14) A cup of oatmeal

(15) One and one-half cups of Special K cereal

(16) One-half cup of cooked rice

(17) Three carrots

(18) Two-thirds of a cup of cooked lentils

(19) A half-cup of cooked kidney or pinto beans

(20) A cup of split pea or bean soup

If ingesting 20-25 grams of carbohydrate every 15 minutes for four hours after a tough workout is just too much of a bother, a modified glycogen-storage plan may work almost as well. According to Mike Sherman, Ph.D., one of the Ohio State investigators and an internationally acclaimed expert concerning carbohydrate's role during exercise, taking in 40-50 grams every 30 minutes or 60-75 grams every 45 minutes might yield similar rates of carbohydrate warehousing.’

The clear message from over a half a century of research on the links between food, nutrition and exercise capacity seems to be that next to natural talent and appropriate training, a high carbohydrate diet and adequate fluid intake to avoid dehydration are the two most important elements in the formula for successful participation in sport. This does however seem to work better in men, and is relevant predominantly to exercise of a longer duration than 90 minutes. I look forward to more research in this field targeted specifically to female athletes.