One thing’s for certain in the world of nutrition and food lifestyle, it’s complicated. There are myriad, wildly different diets, many claiming fantastic results if you “just buy their product” that may or may not offer any clinical evidence to support their claims. In order not to be another flashy voice “selling a product” I aim to briefly cover the ketogenic diet, how it changes brain chemistry, and what this may mean for obesity and other health concerns.
First, what is the ketogenic diet?
Distinct from the typical U.S.A high carb diet, the ketogenic diet is high-fat and low carb, which shifts the body from using carbohydrates as the primary fuel to using ketone bodies as fuel source #1. You might be asking, what are ketone bodies? Ketone bodies are small intermediates in fat metabolism that can be used by the brain as an energy source! Historically, the keto diet has been used as an epilepsy treatment (for about a century) and is experiencing a medical renaissance, being looked at as a treatment for Alzheimer’s Disease, Multiple Sclerosis, Cancer, Parkinson’s Disease, and Autism Spectrum Disorder!
With so much work being done across various diseases, key questions are how does the ketogenic diet impact brain chemistry, and (for our purposes) how these changes might be useful in the context of obesity.
The ketogenic diet has been shown to 1) reduce hunger and 2) increase fatty acid oxidative metabolism—which both converge to overall decreases in body fat. This intuitively makes sense; if I’m less hungry and eating fewer calories while also burning more fat (and burning it more efficiently) I’m going to lose fat mass compared to my baseline.
What is sometimes harder to grasp is how eating fat can decrease fat—doesn’t fat make people fat? The trick is, in the context of the ketogenic diet, because carb intake is so low the body shifts into ketosis—where fats are the primary source of energy, not carbs. Typically, the brain loves sugar (glucose) as the preferred energy source. So when I eat a high-fat, high-carb diet the carbs are immediately metabolized into energy while the denser, more energy-rich fats are sent to storage in adipocytes (fat cells). When we were hunter/gatherers this made sense, store as much energy as possible because who knows when the next meal will come. In today’s hyper-modern world where those not experiencing food insecurity have easy access to cheap, calorie-dense food (think fast food), the body consuming many more calories than it can burn and stores the energy as fat.
This means that while in ketosis, I don’t have access to any glucose, therefore fats are the next most readily available fuel. This is why people can live healthily and decrease body fat while eating a high-fat, low-carb diet.
The ketogenic diet does not stop here, there are other neural consequences(think neuroinflammation) that come from removing carbs from the diet. First, scientific evidence has shown that a typical high-fat diet can trigger neuroinflammation by increasing pro-inflammatory cytokines (especially IL-1β and TNFα). These cytokines further trigger signaling cascades that result in insulin resistance, which dysregulates signaling pathways that make you feel “full”. This is bad news. Here’s the interesting thing though, other studies suggest that the ketogenic diet actually lowers neuroinflammation by decreasing concentrations of IL-1β and TNFα! What are we to make of this contradictory evidence?
One suggestion I have is that a high-fat diet, while harmful when coupled with high carbs, is beneficial in the context of a very low-carb lifestyle. Here’s the reason. The types of saturated fatty acids that trigger neuroinflammation only stick around too long in the bloodstream because the body is busy metabolizing glucose. During ketosis, those saturated fatty acids are more quickly broken down into ketone bodies, which are directly used by the brain and do not (to the best of my understanding) trigger neuroinflammation like saturated fatty acids.
The take-home messages are first, fats are not “evil”, they’re a fuel source—just like carbohydrates and protein. Second, the role of fats in health and disease ranges widely based on several factors, one of which is what other energy sources are available at a given time. Thirdly, the ketogenic diet has the potential for treating many diseases and as a key tool in situations of morbid obesity to increase fat oxidation. Finally, wrestling with both sides of the harmful/helpful fat debate illustrates that science can be controversial and that critical thinking skills are needed to make sense of contradictory evidence!
