It’s a common question or “problem” that often comes up within the ketogenic community.
Why do some people on a keto diet blow high numbers of ketones while others eating the same way blow low numbers?
Let me offer my exploration of the research, some educated speculation, and actionable advice you can ruminate on.
Why do some people on ketogenic diets produce low ketone readings when they test?
One theory is that some keto-adapted people are so adapted to producing and burning ketones that they don’t leave any extra to spill into the urine and breath. They make only as many as they can use and their cells gobble up almost every ketone they produce. Under this argument, low ketone numbers on a ketogenic diet are a reliable sign of full ketone adaptation.
This sounds plausible, but I haven’t seen any empirical evidence that it’s the case.
Another theory is that the keto-adapted have built so much fat-burning metabolic machinery in their muscles that they can burn free fatty acids directly and don’t require much additional fuel from ketones. They make enough ketones to fuel the brain, since our brain can’t run on fatty acids directly, but your muscles no longer require as many. Many people who have been in long term ketosis can get by quite nicely on 20-30 net grams of carbs a day and might only show .4 or .7 millimolar ketones on a blood test, but they have plenty of energy from burning free fatty acids and maintain muscle mass on relatively fewer calories than when they were dependent on carbs.
Keto pioneers Stephen Phinney and Jeff Volek found that keto dieters blew higher readings early on in the diet when they were still burning ketones in the muscle. As they grew adapted to free fatty acids as a source of fuel and produced ketones primarily for the brain, ketone levels dropped. It was totally normal. If anything, they were more fat/keto-adapted at lower ketone readings.
Consider the energy requirements of the brain. Whether it’s running on glucose (most of the population) or mostly on ketones, the brain is a steady state organ that never spikes energy demand. It’s a slow-burn 24/7 at nearly the same output whether you are sleeping, exercising hard, or concentrating hard. While the brain has a substantial caloric requirement (at roughly 2% of our body weight, it uses 20% of our resting metabolic rate), you don’t need a ton of glucose or ketones at any one time to power your brain gracefully all day long. That’s why people can “get away” with lower ketone production and still reap the benefits we expect from eating this way.
There’s almost certainly a genetic component to ketone production, too. Take the Inuit, who were rarely in ketosis despite traditionally eating a very low-carb diet. It takes several days of deep fasting for them to produce measurable ketones. Yet, they are adept at burning free fatty acids, almost as if they “skip” keto-adaptation and proceed directly to burning fat. Other variants that affect ketone production have yet to be discovered, but they’re out there.
What about people on long term ketogenic diets who still get astronomical readings? What’s going on?
A major factor not often mentioned in whether someone on a keto diet blows high or low ketones is overall calorie intake. How much food are you eating?
Ketones are generated when the amount of dietary fat available to be burned exceeds the supply of oxaloacetate (provided by protein or carbohydrates). It’s not that the body thinks, “This woman needs some ketones, stat.” It’s more like, “I’ve got too much acetyl-COA from all this fat, and I can’t find any oxaloacetate. Guess it’s ketones!” If you’re the type to use keto to justify chugging olive oil, you’ll generate lots of ketones simply because your fat intake is outpacing the supply of oxaloacetate. Keto athletes eating tons of calories will probably produce more ketones simply because they’re eating so much fat.
If you’ve attained the much-desired “caloric efficiency” I espouse and eating fewer calories overall, you’ll generate fewer ketones but still be “keto.”
Another factor is the use of exogenous ketones. Dean Ornish could take keto esters and blow big numbers.
Above all else, focus on the symptoms.
Can you go without a meal and maintain steady, even energy and concentration?
Are you losing body fat or happy with your body composition?
Are you thinking more clearly?
Has the keto flu come and gone?
Are aerobic activities easier than ever?
If any of those are happening to you, there’s no need to fret over some numbers on a device. The numbers can’t negate your real world experience.
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