Study Critique: Low Carb Diet Improves Memory

This study attempts to draw conclusions between a low-carb (ketogenic) diet, and enhanced memory function. Their conclusions are that a ketogenic diet is protective because of the lower insulin levels it secretes. In this post, I’ll take a look at the other hormones at play, and try to find out what might be the real cause for the memory improvement. Seems like a good time, let’s see how it measures up…

Take a look at the graphical data below from the study. Clearly there was a memory improvement after the low-carb meals. Makes it easy to put the blame on insulin, huh?

But, what else might be going on here? We know there must be other hormones at play. Notice the breakdown of each meal below, and take note on the amount of protein in each one. They are very close, basically the same for the purposes of this study.

I’ve said previously that protein actually enacts a higher insulin response than carbohydrate. Since both meals in the study kept protein relatively the same, the insulin response from the high-carb meal could only be a result of the higher carbs. I suspect that, had the low-carb diet used the same amount of protein (a good estimate of the average low-carb meal), and the high-carb diet used half the amount of protein (about 30 g. a more realistic amount for the Standard American Diet), the researchers would have observed a higher insulin response in the low-carb meal, or even an insignificant difference in insulin response.

Now, introducing Ghrelin, a wonderful hormone indeed.

Ghrelin production ramps up when you become hungry and during periods of fasting

  • It increases secretion of growth hormone
  • It increases focus and cognitive function
  • It increases cardiac output
  • It increases the amount of dopamine in the brain’s center of reward and addiction

If you don’t believe me, just Google it.

So normally, once you eat, ghrelin will decrease, and insulin will increase. Here is where satiation kicks in, and you start to feel satisfied, relaxed, calm, and possibly a bit fuzzy, depending on what exactly you ate.

Now I’ll try to show you how insulin alone is not the reason for the difference in cognitive function. This study shows the different levels of ghrelin responce across 3 breakfast meal types: a  high calorie simple carb, a  high calorie complex carb, and a low calorie meal (water).

Ghrelin concentrations decreased after the HC-SC breakfast by 41%, after the HC-CC breakfast by 33%, and after the LC breakfast by 24%. No significant differences in ghrelin concentration among the 3 breakfasts were observed until 120 min. Ghrelin concentrations were correlated with subjective measures of hunger (r = 0.51) and fullness (r = –0.44). The percentage decrease in ghrelin between 0 and 30 min was inversely correlated with the percentage increases in insulin (r = –0.76) and glucose (r = –0.79) but not with changes in leptin (r = 0.10). The percentage changes in ghrelin concentrations between 30 and 180 min were correlated with the percentage changes in insulin (r = –0.53) and leptin (r = –0.47) but not with changes in glucose (r = 0.22).

The big high calorie simple carb meal would have likely been the equivalent of pop tarts, waffles, syrup, or any combination of cereal grains covered in sugar. You know, the processed food-like crap that millions of ignorant parents shovel into their kid’s mouths before they run off to school.

The high calorie simple carb meal suppressed ghrelin more than either of the other two meals. The simple-carb meal would have enacted the largest spike in blood glucose levels, with the largest decrease in cognitive function, motivation, clarity, etc, flooring levels of ghrelin. Although the responses to ghrelin were inversely correlated with insulin levels, I assume that is because the 3 meals also had similar protein amounts, making the difference in insulin response only a result of the amounts of cheap carbs across the meals.

Want to stay sharp and focused in the morning? Tired of the mid-afternoon slump after lunch? Try limiting blood glucose spikes by eliminating sugar, bread and cereal from your diet. Eat only things that will keep you on the cognitive razor’s edge: meat, veggies, fruit.


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