Breakfast cereal and exercise

“A bowl of cereal beats guzzling an expensive sports drink after a workout,” the Daily Mail has reported. The newspaper said that “the breakfast snack was at least as good, if not better, at revitalising muscles”.

In this research, a team of scientists from the University of Texas gave either cornflakes or a sports drink to eight male and four female athletes after a typical exercise session. The researchers analysed blood samples and muscle tissue to try to understand the effects of the two foods on revitalising muscle, particularly the way the body replaced glycogen, the fuel for muscle, or built up the muscle protein itself.

Overall, this small laboratory study provides reasonable evidence that some aspects of protein synthesis were the same, or perhaps better, after a recovery food of wholegrain cereal compared to a sports drink. It supports the authors’ conclusions that, as cereal with non-fat milk is a less expensive option than a sports drinks, cereal can be a wise meal choice throughout the day, not just for breakfast. However, more research is required to determine the best carbohydrate and protein mixture for recovery.

Where did the story come from?

Lynne Kammer and colleagues from the Department of Kinesiology and Health Education at the University of Texas carried out this research. The study was supported by the Wheaties cereal brand and the General Mills Bell Institute of Health and Nutrition. The study was published in the peer-reviewed Journal of the International Society of Sports Nutrition.

What kind of scientific study was this?

This was a non-randomised controlled study that compared how eating cereal with non-fat milk and drinking a carbohydrate-electrolyte sports drink affected the body if consumed immediately following endurance exercise.

The researchers explain that endurance exercise increases protein breakdown and reduces energy, stored as glycogen, in muscles. Replenishing these stores is thought to be important in recovery after exercise. Combined carbohydrate and protein will stimulate the production of insulin, which increases the production of both glycogen energy stores and protein.

For this study the participants were recruited through an email announcement, completing a health questionnaire. Those with heart disease, diabetes or with other high-risk medical conditions were excluded. Volunteers could not be taking regular medications except for allergy or contraceptive pills.

Eight male, trained cyclists or triathletes aged around 28 years (on average weighing 75.4kg), and four fit females about 25 years old (weighing 66.9kg on average) agreed to participate. They were told to perform only light exercise and eat consistently the day immediately prior to the trial.

Each person acted as their own control, meaning that they went through two testing sessions where they were given either the cereal with milk or the sports drink in random order. There were 4-12 days between each testing session. After two hours of cycling, the researchers took a muscle tissue sample (biopsy) from the thigh muscle and then the recruits either drank the sports drink (containing 78.5g carbohydrate) or ate cereal and skimmed milk (with 77g carbohydrate, 19.5g protein and 2.7g fat). A second biopsy was taken at 60 minutes. Blood samples were taken for testing before and immediately after exercise, and then at 15, 30 and 60 minutes after consumption. Blood was collected to test for glucose, lactate (a chemical produced by exercising muscle) and insulin.

The researchers measured fitness by estimating the volume of oxygen that was consumed while exercising to maximum capacity, and used this to give the participants a work rate that was standardised across the recruits.

The differences within and between treatments were tested statistically. The main outcomes of interest for the researchers were the measures of muscle glycogen synthesis and the phosphorylation state of the proteins in the muscle sample (known as Akt, mTOR, rpS6 and eIF4E), which control protein synthesis in the muscles.

What were the results of the study?

An hour after exercise blood glucose was similar between treatments (about 6mmol/L), but after cereal, plasma insulin was significantly higher (191.0picomol/L) compared to after the sports drink (123.1picomol/L). Plasma lactate was significantly lower after the cereal (1.00mmol/L) compared to after the drink (1.4mmol/L).

One of the proteins in the biopsies showed higher phosphorylation (mTOR) after cereal with milk compared to the sports drink, but glycogen and the phosphorylation of the other muscle proteins was not statistically different between the two recovery foods.

What interpretations did the researchers draw from these results?

The researchers conclude that “cereal is as good as a commercially available sports drink in initiating post-exercise muscle recovery”.

They say that while both the wholegrain cereal with non-fat milk and the sports drink increased glycogen following moderate exercise, significant phosphorylation of some proteins only occurred after cereal.

What does the NHS Knowledge Service make of this study?

This research, using a typical cycling endurance workout, has examined the effects of readily available foods and drink on glycogen synthesis and the phosphorylation state of proteins controlling protein synthesis. As a physiological study in selected people it provides useful information, but there are some points to note:

• As a small study of 12 athletes the results may not be generally applicable to everyone. It is possible that trained athletes respond differently to food and drink in the recovery phase after moderate exercise.
• The exact component of the cereal with milk combination that is responsible for the difference between groups is not clear. It is implied that the carbohydrate content between cereal and a 6% carbohydrate sports drink is the key difference. However, it is possible that the milk, containing protein, may be contributing.
• Participants were randomly assigned the order in which foods were taken. This reduced any differences between the intervention and control groups as everyone took part in both arms of the trial. The researchers have adjusted in their analysis for the fact that the comparative data were coming from within subjects rather than between groups. The study does not report how the four women, for example, were split between those given sports drink or cereal first. A larger trial where groups of athletes are randomised to one food or another would provide more convincing evidence.

Overall, this small laboratory study provides reasonable evidence that some aspects of protein synthesis were the same or perhaps better after wholegrain cereal with milk compared to sports drink, but more research is required to determine the best carbohydrate and protein mixture for this.