My question is about exercise and hypoglycemia. When I got home from work this afternoon, I ate 2 fillets of tilapia and an orange. After about 25 minutes, I then began riding a stationary bike. When I had ridden for 26 minutes, my blood sugar all of the sudden took a nose dive: I became faint and light-headed. I ate an apple and a couple handfuls of walnuts and the symptoms disappeared within a few minutes.

Normally I don’t have this problem. I do this type of exercise almost daily. But I usually eat an orange immediately before starting to exercise. Today, I didn’t start exercising until almost a half-hour after eating. Was that the cause of my problem?

I believe that you experienced low blood sugar because of the reduced carbohydrate content of the diet compared to your former diet. First and foremost, listen to your body and if a piece of fruit and some nuts alleviates symptoms then do so.

I believe that one of the metabolic changes that eventually occurs on reduced carbohydrate diets is increased utilization of fat by working muscles. The two primary sources of this fat are 1) fat stores directly within muscle called “intra-muscular triglycerides” (IMT), and 2) free fatty acids in your bloodstream whose source is from stored fat in adipose (fat) tissue. When the typical western, high carbohydrate diet (bread, rice, potatoes, refined sugars etc) is consumed the muscles adapt to this diet by storing more carbohydrate within muscle cells as glycogen, and simultaneously storing less IMT. Additionally, high carbohydrate diets tend to reduce the enzymes that allow fat stores to be broken down and utilized during exercise. As your body becomes more and more accustomed to a reduced carbohydrate intake, both IMT stores will increase along with increased efficiency of stored fat breakdown. Thirdly, liver, blood and muscle glucose stores will be more actively conserved. The net effect of all of these changes will be to keep your blood sugar levels within normal ranges during exercise. I cant tell you specifically how long these changes may take, but my co-author of my next book (The Paleo Diet for Athletes), Joe Friel, a U.S. Olympic triathlete coach, who has adopted the diet, indicated it took him 6-8 weeks.

In support of this notion (increased efficiency of fat utilization during exercise) is evidence from the Ache hunter-gatherers from Paraguay. My research colleague, Dr. Kim Hill from the Univ of NM has spent the last 30 years studying the Ache people and has gone along with the men as they hunt peccaries in the forests. Kim reports that the men frequently would get up in the morning, eat no breakfast and then chase after peccary herds, in hunts that could last 6-8 hours or more. During this time the Ache men took no food and only drank water during the extended chase. Kim said he tried to “run with the hunt” with the Ache men, but could never do it. He always had to have his breakfast to be able to keep up. He told me the Ache men would laugh at him. Apparently, these hunters have metabolic systems that make magnificent use of the fatty acid metabolic pathways. It would be interesting to measure IMT stores, and beta-oxidation pathways (fat breakdown) in the Ache and compare them to westerners.

Anyway, the bottom line is to listen to your body until it is fully adapted to this new way of eating. -FAQ