Ketosis DOES Matter (emerging science behind sustained weight loss) by Troy Lightfoot

Recently I’ve been seeing a lot online “Ketosis doesn’t matter” regarding weight loss. Unfortunately for the authors and YouTubers involved, the science doesn’t seem to agree with their position.

For a simplistic definition, ketosis is when your liver creates ketones to be used for energy. Your liver will create ketones in certain conditions without being in ketosis but clinically a blood ketone reading of 0.5 MMOL or above is seen as nutritional ketosis. At this measurement, you will have needed to keep your carbohydrates low enough for your liver to produce ketones on its own and your body will mainly be using fatty acids and ketones as a fuel source.

I do understand the sentiment behind not focusing on ketone levels. For one, once you are actually in ketosis it doesn’t really matter how “deep” you are to use fat as an energy source. The amount of BHB in your blood doesn’t correlate with the amount of fat loss but for certain medical conditions, it actually does matter. For example, epileptic patients.

Marilyn Strathern described Goddard’s Law with this quote "When a measure becomes a target, it ceases to be a good measure." Blood ketones are just a measure of what’s happening in your blood, they should not be a target to shoot for. Otherwise, you could just take exogenous ketones, raise your blood ketone level to 3.0 and assume that you would be “burning more fat.”

With all that being said actually being in a state of nutritional ketosis does matter scientifically. Before going into the science behind this it’s important to understand the science behind the “Calories In / Calories Out” theory.

The largest clinical trial ever done to test this theory was called the “Women’s Health Initiative.” It followed almost 50,000 women for 7 years as they reduced their fat intake and kept their caloric intake below their “metabolic rate” (This term is another blog post on its own but for now let’s just go with it) The trial costs the US taxpayer over 400 million dollars. This was the study that was supposed to support the low fat, low calorie, “eat less move more” hypothesis. Instead what it proved was that for long term sustained weight loss, it doesn’t work. Over 7 years, women reduced their daily calorie intake by 361 calories per day. They reduced their percentage of calories from fat and increased their carbs. They also increased their daily exercise by 10%.


Note this was a randomized controlled trial. According to the study, the participants adhered to the diet and exercise interventions. Here was the result.


Initially, caloric restriction worked and they lost weight. It doesn’t mean they lost much body fat by the way but they did lose weight. Eventually, they gained it all back while keeping calories low and exercising more. In fact, by the end of the trial, waist circumference size was the same.

This happens because your body isn’t a calorie machine, in fact, it doesn’t even know what a calorie is. The less fuel you give your body the less it will require to use for daily activities aka your “Resting Metabolic Rate.” It’s why people like Jillian Michaels often fail when coaching long term sustained weight loss. Just see the biggest loser long term results. Simply put, if you cut your calories when trying to lose a lot of weight, you will have to keep cutting and cutting to lose weight over time and to keep it off as your body will adjust to your intake. This is obviously unsustainable long term and unhealthy.

So why does Ketosis Matter? Take a look at the following study:


The resting metabolic rate (RMR) decrease, observed after an obesity reduction therapy is a determinant of a short-time weight regain. Thus, the objective of this study was to evaluate changes in RMR, and the associated hormonal alterations in obese patients with a very low-calorie ketogenic (VLCK)-diet induced severe body weight (BW) loss.


Despite the large BW reduction, measured RMR varied from basal visit C-1 to visit C-2, − 1.0%; visit C-3, − 2.4% and visit C-4, − 8.0%, without statistical significance. No metabolic adaptation was observed. The absent reduction in RMR was not due to increased sympathetic tone, as thyroid hormones, catecholamines, and leptin were reduced at any visit from baseline. Under regression analysis FFM, adjusted by levels of ketonic bodies, was the only predictor of the RMR changes (R2 = 0.36; p < 0.001).


The rapid and sustained weight and FM loss induced by VLCK-diet in obese subjects did not induce the expected reduction in RMR, probably due to the preservation of lean mass.

When reading the actual study, the level of ketones in their blood correlated with retention of muscle mass. Meaning they lost body fat, not muscle and kept the metabolic rate the same while losing weight! Another incredible finding “It is noteworthy that despite the considerable weight loss induced by the VLCK-diet, there was a positive nitrogen balance throughout the entire study.” A positive nitrogen balance is seen as the key to muscle growth.


Ketones seem to be protective against muscle loss and in fact promote muscle growth in periods of fat loss.

In the future, I’m going to write a blog post about antioxidants and studies showing ketones are protective against reactive oxygen species without needing to ingest “anti-oxidants” in the form of fruit or plants. That is more about longevity rather than weight loss but the same concept applies. It seems ketosis does matter!