The modern prescription of high carbohydrate, low fat diets and eating snacks between meals has coincided with an increase in obesity, diabetes, and and increase in the incidence of many mental health disorders, including depression, anxiety, and eating disorders. In addition, many of these disorders are striking the population at younger ages. While most people would agree that diet has a lot to do with the development of obesity and diabetes, many would disagree that what we eat has much to do with our mental health and outlook. I believe that what we eat has a lot to do with the health of our brains, though of course mental illness (like physical illness) has multifactorial causes, and by no means should we diminish the importance of addressing all the causes in each individual. But let’s examine the opposite of the modern high carbohydrate, low fat, constant snacking lifestyle and how that might affect the brain.
The opposite of a low fat, snacking lifestyle would be the lifestyle our ancestors lived for tens of thousands of generations, the lifestyle for which our brains are primarily evolved. It seems reasonable that we would have had extended periods without food, either because there was none available, or we were busy doing something else. Then we would follow that period with a filling meal of gathered plant and animal products, preferentially selecting the fat. During the day we might have eaten a piece of fruit, or greens, or a grub we dug up, but anything filling or high in calories (such as a starchy tuber) would have to be killed, butchered, and/or carefully prepared before eating. Fortunately, we have a terrific system of fuel for periods of fasting or low carbohydrate eating, our body (and brain) can readily shift from burning glucose to burning what are called ketone bodies.
It is true that some parts of some brain cells can only burn glucose, but fortunately our bodies can turn protein into glucose through a process known as gluconeogenesis. This fact means that while there are essential requirements for both fat or protein (meaning we would die without eating at least some fat and at least some protein), we can live quite happily while consuming no carbohydrate at all. That’s not saying there aren’t some disadvantages or side effects to a so-called “zero carb” diet, but it won’t cause the massive health problems and death that consuming zero fat or zero protein would.