Many people believe that they need to be ‘in ketosis’ to burn fat. Because ketones rise when someone is burning their body fat, they think that fat loss is due to the ketones, regardless of where they are coming from. Hence, they assume that more ketosis is better, especially if you have body fat to burn.
While this belief helped sell keto-related products such as recipe books and developed a cult-like following of people who believe that keto is the only way, it’s simply not true. Rather than believing that more ketones are better, it’s critical to understand whether the ketones are mainly coming from your body (i.e. endogenous ketosis) because you’re in an energy deficit or from that third buttered coffee (i.e. exogenous ketosis).
Ketones are produced by the liver from the breakdown of fat. This fat can come either from your body or your diet.
Your body typically burns fat in the citric acid cycle, but it requires oxaloacetate (from carbs and/or protein) to do this. Ketosis is simply an alternative metabolic pathway that your body can use when there is less oxaloacetate in your diet (from carbs or protein) to burn fat via the citric acid cycle.
So, when carbs and protein are low, the fat that can’t be oxidised in the citric acid cycle is oxidised via ketosis. The image below (prepared by Amy Berger) shows this graphically. On the right, we have the default process, while on the left we have ketosis, which occurs when there is inadequate oxaloacetate.
This backup metabolic pathway has helped humans survive many a famine. When our energy levels are low, we see an upregulation of mitochondrial biogenesis, sirtuins, autophagy and the NAD+:NADH ratio, which is highly beneficial. Our body goes into repair mode to ensure survival, and we switch over to burning body fat. However, while many glorify ketosis as a magical state and talk about the many benefits, we often miss the fact that most of the benefits are NOT necessarily due to the ketones themselves, but rather, the energy deficit that is associated with endogenous ketosis.
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