Fruit, Insulin Release and Meat

This is a picture of my fruit bowl. This is just a portion of the fruit I eat during a week. Not shown are all the frozen fruits and berries I also eat during the week. I think fruit is an athlete’s best friend (or anybody’s for that matter). It is fast food at its best. All it requires is washing and maybe peeling (and perhaps thawing). It is high in water, fiber, and nutrients. It even has protein. It is great fuel for the muscles and the brain. And at 300 calories per pound, you can eat as much as you want and you won’t go into caloric excess. Just by way of comparison, 13 apples have the same number of calories as one 7oz bag of potato chips. Yup, when you eat whole, natural plant foods, it is really hard to eat too many calories.

But for some reason fruit has been given a bad rap by some of the popular low carb diets. If I had a dollar for every time someone said, “but doesn’t fruit have a lot of sugar?” I would be rich (or at least richer than I am now). I have yet to see a single study that shows that eating too many berries, or apples, or bananas causes obesity. If anything, I see the opposite, that fruit intake is associated with weight loss over time.

We are actually designed to eat sugar. I know, that sounds like blasphemy since sugar has become the latest dietary evil. But we are attracted to and enjoy foods that are sweet. There is a good reason for this. Our brains are glucose hungry organs and sugar is its primary fuel source. Our muscles burn glycogen (or stored sugars) during exercise, especially during intense exercise. And, if we want to burn fat, well we need sugar to do that (check out glycolysis and beta oxidative pathways if you don’t believe me). Finally, if you eat a high protein diet, your liver speeds up a process known as glyconeogenesis, which is a fancy way of saying it cranks up sugar producing mechanisms. This suggests to me our bodies prefer adequate carbohydrates over excess protein.

Sugar is what we run on.

But we do need to eat sugar that comes well packaged with fiber and nutrients and water. Yes, the food complex it comes with is important. Remove the nutrients and water and fiber and you end up with a very concentrated, hyper-palatable, calorie dense substance that we really shouldn’t be eating (unless you are eating it during 5 hr runs or bike rides).

But insulin is released in response to eating carbohydrate rich foods, right? And isn’t it insulin that makes us fat? This is the entire theoretical framework upon which many low carb diets are based. Carbs produce insulin, insulin makes you fat and therefore carbs make you fat.

This carbohydrate insulin model (or CIM) of obesity just doesn’t hold up to scrutiny very well. The premise of the CIM is that carbohydrate intake is the primary cause of human obesity and that insulin is its primary effector. First of all, the primary job of insulin is to get glucose into cells. The second role of insulin is to get amino acids into cells. Its third role is to promote fat uptake into fat cells. Thus, insulin has important functions on many fronts, the least of which is fat deposition.

A recent 12-month study (randomized clinical trial) looked at the predictive value of glucose-stimulated-insulin secretion on weight-loss in response to a low-fat or a low-carb diet in overweight adults. Despite large and sustained differences in glycemic load, weight loss did not differ between the diets and insulin secretion had no predictive value regarding weight loss. To quote one paper, “…the hypothesis that carbohydrate stimulated insulin secretion is the primary cause of common obesity via direct effects on adiposytes is difficult to reconcile with current evidence."

Now it is true that too much insulin is not good for lots of reasons. Chronically high levels of circulating insulin increase risk for cancer. It is also not good for the brain. 

But what few people realize is that carbs aren’t the biggest offenders when it comes to insulin release.

To quote one of my favorite authors and nutrition research gurus Dr Greger;

“What they [low carbers] overlook is that "protein- and fat-rich foods may induce substantial insulin secretion" as well. Research in which study subjects served as their own controls, for example, has shown that under fasting conditions a quarter pound of beef raises insulin levels in diabetics as much as a quarter pound of straight sugar. Atkins' featured foods like cheese and beef elevated insulin levels higher than "dreaded" high-carbohydrate foods like pasta. A single burger's worth of beef, or three slices of cheddar, boosts insulin levels more than almost 2 cups of cooked pasta. In fact a study in the American Journal of Clinical Nutrition found that meat, compared to the amount of blood sugar it releases, seems to cause the most insulin secretion of any food tested.” [American Journal of Clinical Nutrition (1997):1264. Diabetes Care 7(1984):465. American Journal of Clinical Nutrition 50(1997):1264. American Journal of Clinical Nutrition 50(1997):1264.]

Whole fruit on the other hand, does not spike blood sugar levels or insulin for that matter.

Now that we have that misconception cleared up my next section I will talk about why fruit is so good for us and ways to eat more.