Research Update: High Glycemic Carbs And Your Brain

Effects of dietary glycemic index on brain regions related to reward and craving in men. American Journal of Clinical Nutrition 2013; 98(3):641-47.

Objective

The goal of this investigation was to examine the effect of glycemic index on brain function during the late post-prandial period (4-5 hours after eating a meal).

Methods

Twelve overweight men consumed two liquid meals on separate occasions. The meals were identical in calories, macronutrients, and palatability. The only difference between the meals was that one had a glycemic index of 84, and the other had a GI of 37. Brain activity was then measured by MRI four hours after consumption of each meal. Blood glucose, insulin, and hunger were also measured repeatedly during the post-prandial period.

Results

Plasma glucose was significantly lower and hunger was significantly greater four hours after the high glycemic meal when compared to the low glycemic meal. The high glycemic preload also elicited a greater brain activity centered in the right nucleus accumbens. This area of the brain is associated with reward and food craving.

Comment

This is a fascinating study! We’ve known for years that high glycemic carbs promote a post-prandial dip in blood sugar that leads to an increase in hunger. I always thought that this was governed solely by the endocrine system. This is the first study to show that high glycemic carbs actually change brain activity, particularly in areas that control reward and craving. While this is just one study, it was very well designed.

Take Home Message

If you work with me or have read my books, you know that a low glycemic approach is the key to losing weight and improving health. This study provides even more reason to strictly limit high glycemic carbs like bread, pasta, white rice and sugar. Instead, focus on lower glycemic carbs like fruits, vegetables, legumes, and whole grains.

 

Should eggs be a part of your regular diet?

The controversy surrounding the egg is a great example of the divide between popular opinion and well-designed research in the field of nutrition. Eggs have been vilified for decades because of their high cholesterol content. Many doctors and nutritionists advocate complete avoidance of egg yolks. I recently read a well written review of the current literature on eggs and health in The American Journal of Clinical Nutrition (1). I definitely learned a few new things.  Therefore, I thought that an update on the research concerning eggs and our health would be a great feature article for the 1^st edition of this newsletter.

Why Have Eggs Been Vilified?

Eggs are considered unhealthy for one basic reason: they are high in cholesterol. A single egg has 213 milligrams. The daily recommended intake for dietary cholesterol is 300 mg. per day. Therefore, by consuming 2 eggs at breakfast, you exceed your daily recommendation for cholesterol. The theory behind the advice to avoid eggs is that consuming too much dietary cholesterol will increase risk of heart disease and stroke.

Research On Eggs And Disease

The article I mentioned earlier is a comprehensive review and meta-analysis of all research to date on the association between eggs and our health (1). In a meta-analysis, researchers combine data from many different studies in order to calculate a statistical summary of all published research. It is kind of like dumping all of the subjects from all of the studies into one population and then analyzing the data.

When this was done for eggs, the researchers found no increased risk of heart disease, stroke, or total cardiovascular disease when comparing those consuming one or more eggs per day to those eating less than one egg per week. This is not new or surprising. Past research has shown that dietary cholesterol is only weakly associated with serum cholesterol. In the Nurses’ Health Study, the Health Professional Follow-up Study, and the Framingham Heart Study, there was no association between egg consumption and risk of heart disease (2,3).

However, the meta-analysis found a 42% increased risk of type 2 diabetes when comparing those consuming one or more eggs per day to those consuming less than one egg per week. This was news to me and I found it a bit disturbing. Therefore, I went out and retrieved all of the major studies on eggs and type 2 diabetes and read them for myself.

I found 5 studies, 3 prospective cohort studies (4-6) and 2 randomized controlled trials (7,8). One of the prospective cohort studies showed a 58% increased risk of type 2 diabetes when comparing subjects consuming 1 or more eggs per day to those consuming less than one egg per week (4). The other 2 cohort studies showed no association (5,6).

The 2 randomized trials were of similar design and were conducted by the same research group (7,8). These trials found that consuming 3 eggs per day for 12 weeks did not raise fasting glucose or insulin resistance.

After reviewing the studies, I came to the conclusion that there is far more evidence that eggs do not increase the risk of type 2 diabetes than that they do. However, the study that showed an association was well designed, so we will keep our eyes on this area of investigation.

What Else Is In Eggs Besides Cholesterol?

An egg yolk is very much like a multivitamin supplement. It contains vitamin D, folate, vitamin E, vitamin A, monounsaturated fat, vitamin B12, vitamin B2, essential amino acids, linoleic acid, calcium, and vitamin B1. Egg yolks are, in fact, one of the most nutrient dense foods that you can eat.

Recommendation

I tell my clients to enjoy up to 6 egg yolks per week. This amount does not have any negative impact on cardiovascular disease and will absolutely pack their breakfast with protein and essential nutrients. There are 2 populations that I would alter this recommendation for:

1) Diabetics: There is evidence of an increased risk of heart disease in diabetics that consumed 1 egg per day (2). Therefore, if you are diabetic, I would limit egg yolks to 3 per week.

2) Older men with a diagnosis of prostate cancer: There is some preliminary evidence of an association between consuming 6 or more eggs per week and an increased risk of progression from more benign prostate cancer to a more deadly form (9). There is no evidence of this association for men consuming up to 3 yolks per week. While this area of research is not yet definitive, I’d play it safe and limit myself to 3 eggs per week if I was diagnosed with prostate cancer.

References

1) Shin, et al. Egg consumption in relation to risk of cardiovascular disease and diabetes: A systematic review and meta-analysis. American Journal of Clinical Nutrition 2013; 98:146-59.

2) Hu, et al. A prospective study of egg consumption and risk of cardiovascular disease in men and women. Journal of the American Medical Association 1999; 281:1387-94.

3) Daubes, et al. Eggs, serum cholesterol and coronary heart disease. American Journal of Clinical Nutrition 1982; 36:617-25.

4) Djousse, et al. Egg consumption and risk of type 2 diabetes in men and women. Diabetes Care 2009; 32:295-300.

5) Djousse, et al. Egg consumption and risk of type 2 diabetes in older adults. American Journal of Clinical Nutrition 2010; 92:422-27.

6) Vang, et al. Meats, processed meats, obesity, weight gain and occurrence of diabetes among adults: Findings from Advent Health Studies. Annals of Nutrition and Metabolism 2008; 52:96-104.

7) Mutungi, et al. Dietary cholesterol from eggs increases plasma HDL cholesterol in overweight men consuming a carbohydrate restricted diet. Journal of Nutrition 2008; 138:272-76.

8) Ratliff, et al. Carbohydrate restriction reduces insulin resistance and plasma leptin without modifying appetite hormones in adult men. Nutrition Research 2009; 29:262-68.

9) Richman, et al. Intake of meat, fish, poultry, and eggs and risk of prostate cancer progression. American Journal of Clinical Nutrition 2010; 91:712-21.