The easiest way to explain ketones is with an analogy. Fats are to ketones what carbohydrates are to glucose (i.e., carbs :: glucose = fats :: ketones). Meaning, ketones are the energy source produced by your body from digesting fat molecules whereas glucose is the energy source produced by your body from digesting carbohydrate/sugar molecules.
**Note, for simplicity's sake, I call ketone bodies "ketones" but if you're curious about the semantics go here.
If you've ever tried a low carb, high fat diet (such as Atkins), you've probably experienced what's called nutritional ketosis. Nutritional ketosis is when your body burns fat for energy instead of carbs and sugar. For reasons that may seem obvious, this is good for weight loss -- fat stores are being burned, hallelujah! But the real reason your body does this is not to make you look better in a swim suit: it relates to our body's survival mechanisms.
When a person eats carbohydrates their body stores excess energy as fat through a process called de novo lipogenesis (aka "DNL" or simply "lipogenesis" and translated from latin as "new fat creation"). This is an evolutionary advantage for humans (and other animals as well) because it allows carbohydrates to be stored as fat, which is a much more energy-dense and efficient molecule than a carbohydrate (more on this another time), and to be used for energy when food is in scarce supply. The hormone insulin plays a key role in this process by regulating and promoting the absorption of sugar/carb molecules from the blood to fat tissue and to a lesser extent skeletal muscles. Insulin also signals to brain to KEEP EATING because this delicious carbohydrate/sugar treasure trove is a food source that can be stored by the body for energy later (in the form of adipose tissue aka love handles).
Conversely, when a person eats fat, leptin plays a greater role than insulin. Leptin, also known as the "satiety hormone," tells your brain you are full. Leptin is the reason you can drink an 8 oz glass of skim milk, but not of heavy cream (or if you do, you're not hungry after drinking that full glass of heavy cream). All that fat in heavy cream is causing leptin to hold up it's stop sign to the brain. (Fun fact: heavy cream does not have any milk sugar, aka lactose, whereas skim milk is full of it).
There's another important hormone at play here: ghrelin, also known as the "hunger hormone." When your stomach is empty, ghrelin sends a message to your brain that you need to look for food. If you go without food long enough, your body switches to a "starvation response" which is a set of adaptive biochemical and physiological changes that slow your metabolism in response to a lack of food.
Your body will also fall into starvation ketosis. Starvation ketosis is when your body burns your fat stores. However, starvation ketosis operates in tandem with your body's starvation response. Your body is burning your fat stores, but doing it slowly because it wants to prolong your energy stores as long as possible since it's received news that your next meal is uncertain.
From Dr. Attia: "The reason a starving person can live for 40-60 days is precisely because we can turn fat into ketones and convert ketones into substrate for the Krebs Cycle in the mitochondria of our neurons. In fact, the more fat you have on your body, the longer you can survive. As an example of this, you may want to read this remarkable case report of a 382 day medically supervised fast (with only water and electrolytes)! If we had to rely on glucose, we’d die in a few days. If we could only rely on protein, we’d live a few more days but become completely debilitated with muscle wasting."
Dr. Attia again: "Why do we make ketones? For starters, it’s a vital evolutionary advantage. Our brain can only function with glucose and ketones. Since we can’t store more than about 24 hours worth of glucose, we would all die of hypoglycemia if ever forced to fast for more than 24 hours. Fortunately, our liver can take fat and select amino acids (the building blocks of proteins) and turn them into ketones, first and foremost to feed our brains. Hence, our body’s ability to produce ketones is required for basic survival."
As opposed to starvation ketosis, nutritional ketosis is when you are eating dietary fat and restricting carbohydrates to approximately 20-50 grams per day and maintaing modest (but not high) protein intake. When I first discovered nutritional ketosis (about two years ago now), I felt like I'd reached nutritional enlightenment. At times, I probably give ketosis too much credit, but I can say for certain that being in ketosis changed my body, my energy, and my life for the better. My experience with ketosis has been incredibly positive, perhaps that's not the case for everyone, but I also think we simply don't have enough research on the topic. Switching from a glucose-based diet to a ketogenic diet is not for the faint of heart: it requires a lot more preparation and research than simply eating bacon and butter. I hope this post was a good introduction to ketones and ketosis, but since it's fairly length already, I'll save the ins and outs of nutritional ketosis for my next post. Hopefully, this post helped get my writer's block out of the way and I can gain some momentum on this topic!
