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How a Ketogenic Diet May Influence Body Composition

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Quick Summary tl;dr

As evidenced by the studies above, regardless of whether you lift weights, run, or are just getting started, nutritional ketosis will not hinder your progress and it may even incur some body composition benefits.

Not sure how to get started? There are a ton of great recipes on this site, and if you’re not sure if your diet is ketogenic, one of the easy things about this way of eating is there’s an easy test! Just purchase a ketometer or some ketone strips to measure ketones in your blood or urine, respectively. Easy peasy! You’ll probably only end up doing this a few times to get the hang of it, and that’s fine.

As far as exercise goes, start light and easy, and either progress very slowly or see a professional trainer or coach. As shown in a recent exercise study on low vs. high carb, inexperienced lifters can get injured pretty rapidly if the program is too advanced ( Tay et al., 2018).

Table of Contents

Many trainers, even those open to low carbohydrate and otherwise ketogenic diets, still profess the myth that carbohydrates are required to fuel activity at the ‘high end’ of the intensity spectrum.

This is a testable hypothesis and has been falsified. Further, regardless of changes in hydration status, fat loss is a common occurrence in many of these studies… and many times unwittingly.

The Latest Study on the Effects of the Ketogenic Diet on Body Composition

Most of what we'll discuss is based on a latest study: Extended ketogenic diet and physical training intervention in military personnel ( LaFountain et al., 2019).

As suggested in the title, this was conducted in relatively healthy military personnel. They were physically active but not experienced with “free-weight resistance exercise and Olympic lifts for whole body strength and power.”

How a Ketogenic Diet May Influence Body Composition

Self-Selected Keto vs 'Usual' Diet

The participants self-selected whether to go on a ketogenic diet or maintain their usual diet. This is a nuanced decision. ‘Self-selection’ is usually used in the context where minimizing attrition is a big problem. And as we’ve seen in numerous keto studies where they actually measure ketones, they start out high and inevitably decline as the study progresses.

In theory, individuals who self-select to a ketogenic diet are more motivated to stick with it and this was exemplified in this study. Ketones were maintained around ~1.2 mM throughout the duration of the study.

Why Too Much Protein Won't Kick You Out Of Ketosis

In this study, protein was initially restricted to ~90 grams per day. That was not really necessary in my opinion. Many people can maintain adequate levels of ketones on much higher levels of protein especially when exercising and in an energy deficit.

Most of the protein is used for protein synthesis and the leftover is:

  • oxidized (if in an energy surplus),
  • or stored as liver glycogen (the carbon skeletons) and metabolized into urea (the nitrogens).

Higher protein alone in the absence of an energy surplus does not ‘kick you out of ketosis.’ That said, higher protein may even be more favorable in this context due to the muscle-retention and appetite-suppressive effects.

How a Ketogenic Diet May Influence Body Composition

How Did Keto Affect Exercise Performance?

In those who self-selected to maintain their usual diet, the effect we are going to see over the 12-week study period is primarily due to the exercise intervention alone. In those on keto, we are going to see the effects of keto plus exercise.

If nutritional ketosis somehow impairs physical performance, we would expect this to negatively influence some aspects of their training ultimately resulting in reduced gains compared to the control group.

Back to the study: a lot of the foods were provided — this helps to ensure the diet was ketogenic but also educates the participants on what a ketogenic diet looks like.

Significant Fat Loss in the Keto Group

What happened during the study? One thing that inevitably happens is weight loss. More specifically, fat loss in those who self-selected a ketogenic diet. A lot of fat loss. Over 10 pounds in 12 weeks! Lean mass took a small hit, down about 3 pounds, but this brings up another interesting aspect…

1-rep max in the squat and bench press, force and power output, sprint performance, a ‘military-specific obstacle course’ — All. Completely. The Same.

One potential critique is that these are largely ATP-dependent and don’t rely on muscle glycogen. To that I’d say:

  1. you’re assuming glycogen is reduced in nutritional ketosis but this isn’t always the case; and
  2. maybe these tests aren’t glycogen-dependent, but a lot of the training they did over the last 12 weeks was, and if that impaired their training, then surely they wouldn’t have made just as much progress as the control group.

How a Ketogenic Diet May Influence Body Composition

Did the Keto Group Lose 3 Pounds of Muscle Mass?

Those following a keto diet lost 3 pounds of muscle but still made as much progress fueled by ketones. If I were a speculative man, this is where I’d start speculating.

Another possibility is the unanswered question about dehydration when muscle is apparently lost on a carbohydrate-restricted diet. The theory is that glycogen storage draws a lot of water in muscle, and glycogen is lost when dietary carbohydrates are restricted, therefore the reduced muscle is not reduced muscle proteins but rather simply a loss of water.

Some facts to keep in mind:

  • Not every study shows reduced glycogen in ketoadapted people; therefore the very premise may be flawed and thus overall not applicable.
  • Also, physical performance, exercise capacity, etc., is not hindered in these studies. In that light, and the small overall quantity of muscle we’re talking about, can it really be questioned if it’s a qualitatively important amount of real muscle loss? If any functional parameters declined, I’d be concerned. They are not, so I am not.

More Studies on the Effects of the Ketogenic Diet on Body Composition and Performance

This is NOT isolated finding. Less than a year ago we had this study: A low-carbohydrate ketogenic diet reduces body weight without compromising performance in powerlifting and Olympic weightlifting athletes ( Greene et al., 2018).

It's a similar study design albeit with more experienced lifters. Comparable performance on keto in a 3-month crossover study.

And on there is also a similar study on endurance exercise ( Sansone et al., 2018).

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Bill Lagakos, Ph.D.
Nutritional sciences researcher, consultant and blogger

Bill Lagakos

Hi, I’m Bill. I have a Ph.D. in Nutritional Biochemistry and Physiology from Rutgers University where my dissertation focused on fatty acid-binding proteins and energy metabolism. I studied inflammation and diabetes at UCSD. And most recently, I studied circadian biology at the Mayo Clinic. I have a broad range of knowledge about health, wellness, sickness, and disease... and I’m learning more every day!

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