Everyone knows that eating breakfast is the best way to start the day, right? According to Kaiser Permanente’s health education materials: “This isn’t just a theory; it has been proven by many scientific studies. One six-year study, for instance, measured the mental and physical efficiency of a group of adults throughout the day. Some of the people tested ate good nutritious breakfasts while others did not. When compared to those who ate breakfast, those who did not became less efficient as the day went on. Their efficiency improved after eating lunch, but they slowed down again later in the day and fell behind those who had eaten breakfast in completing their work.” In addition, research has shown that children who regularly eat breakfast have better standardized test scores, better behavior, and are less hyperactive than children who skip breakfast.

The American Dietetic Association’s Fact Sheet on Nutrition suggests that you should “Start your day with a healthy breakfast. Total nutrient intake for the day is usually higher for children and adults who eat breakfast. A breakfast of whole grain cereal, milk and 100 percent orange juice can provide 100 percent of the vitamin C, 33 percent of the calcium and a good supply of folate and other nutrients for a day.”

However, the big brains over at NewScientist want you to know that “eating breakfast can sometimes be worse for mental and physical performance than going hungry.” This month’s NewScientist has a feature piece by Richard Lovett on a Nutrition Bulletin article written by Leigh Gibson that analyzed the cognitive effects of three different kinds of breakfast: Nothing, Something Sugary, and Something Healthy. More specifically, Gibson looked at the effects of eating a breakfast consisting of foods that are high on a Glycemic Index scale versus foods with a low GI value and/or no food at all.

The glycemic index (GI) is a scale indicating how much of a rise in circulating blood sugar (glucose) a carbohydrate triggers. The higher the number, the greater the blood glucose response. So a low GI food should cause a small rise, while a high GI food may cause a dramatic spike. Incidentally, a GI value tells you how rapidly a particular carbohydrate turns into sugar. It doesn’t tell you how much of that carbohydrate is in a serving of a particular food. You need to know both things to understand a food’s effect on blood glucose. That is where glycemic load comes in. The glycemic load (GL) is a relatively new way to assess the impact of carbohydrate consumption that takes the glycemic index into account, but gives a fuller picture than does glycemic index alone. The carbohydrate in watermelon, for example, has a high GI. But there isn’t a lot of it, so watermelon’s glycemic load is relatively low. (For as close to a comprehensive list as exists of single-food GI and GL values, the reader can visit diabetes health advocate David Mendosa’s website).

In Gibson’s study, two cognitive tasks were compared: Delayed recall of a word list, and reaction times when deciding if a word presented on a computer screen matched the color of the word presented (what is known as a Stroop color-word test). Not too surprisingly, people who ate the healthy (low sugar) breakfast performed best on the word recall task. Somewhat more surprising (at least to me) was that people who had nothing for breakfast performed better (i.e., fastest) on the decision task. However, neurobiologist Tamas Horvath at Yale’s School of Medicine was less surprised, noting in the article “Being hungry promotes your awareness of your environment. If you think about a cheetah – how it picks the prey and pursues it – it obviously does it when it’s hungry. A hungry animal is much better at responding to visual and olfactory cues.”

So, it would appear that eating a healthy, low GI breakfast makes you smart, and being hungry makes you alert. Conversely, eating a sugary, high GI breakfast seemed to offer some benefit over fasting in regards to recall, and some benefit over being full of muesili in regards to decision speeds. Cold pizza – that breakfast stalwart for the dorm-bound denizens of our institutions of higher learning – has an admirable glycemic index value of 36 (compared to about 42 for the Muesili used in Gibson’s study). You may draw your own conclusions.

However, the authors of the original article are careful to point out that there is great individual variability in the impact of foods on blood glucose levels. Indeed, the very concept of the Glycemic Index, especially in regards to the effects of fad diets, has itself been challenged rather broadly because the amount of glucose which follows from eating carbohydrate laden foods varies greatly based on both food combinations and individual attributes. Clearly, diabetics are at the extreme end of the spectrum in regards to being most strongly effected by specific foods due to a lack of the glucose-regulating production of insulin in the body. However, it is not clear to what extent “healthy” adults are largely insensitive to the cognitive effects of eating different foods due to the effectiveness with which their bodies regulate this sytem.

No word yet on what kind of breakfast makes your co-workers find you most pleasant to be around, but I’m betting on something containing a lot of bran.

Further Reading:

Gibson, E. L. (2007). Carbohydrates and mental function: feeding or impeding the brain? Nutrition Bulletin, Volume 32, Supplement 1, March 2007 , pp. 71-83(13)

Murphy JM, Wehler CA, Pagano ME, Little M, Kleinman RE, Jellinek MS. “Relationship Between Hunger and Psychosocial Functioning in Low-Income American Children.” Journal of the American Academy of Child and Adolescent Psychiatry, February, 1998.

R.E. Kleinmana, S. Hallb, H. Greenc, D. Korzec-Ramirezd, K. Pattonb, M.E. Paganoe, J.M. Murphy (2002). Diet, Breakfast, and Academic Performance in Children. Annals of Nutrition & Metabolism Vol 46 (Suppl. 1):24-30