A recent study from Australia concluded that keto and other low-carb, high-fat diets may negatively impact bone health in athletes and people who exercise for health reasons.
But should you worry?
In this article, you’ll learn about the latest keto bone health study, possible limitations of the study, what other research has to say on the matter, and keto-friendly tips to keep your bones strong and healthy for life.
Starting in 2016, researchers from several different Australian universities and funded by a research grant from Australian Catholic University recruited 32 elite race walkers for a study on the effects of the keto diet in endurance athletes.
First, the researchers allowed the athletes to choose between a high-carb diet (about 70% of calories from carbs) or a very-low-carb, high-fat keto diet (about 30 grams of carbs per day) for the duration of the study.
Then, over three and a half weeks, the athletes performed monitored exercise sessions as part of their training regimen.
Additionally, during this time, the researchers checked the athletes’ blood for some markers associated with bone health:
- Cross-linked C-terminal telopeptide of type I collagen (CTX)
- Procollagen 1 N-terminal propeptide, (P1NP)
- Osteocalcin (OC)
Also, after finishing the initial trial, some of the low-carb, high-fat diet subjects participated in a “restoration” phase, where they ate a high-carb diet so the researchers could detect any additional changes.
So what were the study findings?
The low-carb, high-fat diet increased post-exercise levels of CTX, a marker of bone resorption (bone breakdown into calcium, which is absorbed into the bloodstream), compared to the high-carb diet.
And compared to baseline, the low-carb, high-fat diet also decreased levels of P1NP and OC, markers of bone formation and metabolism.
Unfortunately, elevated CTX levels and decreased P1NP and OC levels are not good signs.
After the restoration phase, post-exercise CTX decreased to normal levels in the low-carb group, but P1NP and OC levels did not increase to normal levels.
As a result of their findings, the researchers who conducted the study wrote that for athletes, keto “may be detrimental to bone mineral density (BMD) and bone strength, with major consequences to health and performance.”
Limitations of the Keto Bone Health Study
Before you worry about your bone health on keto, and before we take a broader look at the existing research on keto and bone health, let’s start by looking at some limitations and potential flaws of the Australian study.
Bone Markers, Not Bone Density
First of all, the researchers didn’t examine bone mineral density.
Before anyone can draw any real conclusions about the effects of the keto diet on bone health in endurance athletes, a follow-up study that actually measures bone mineral density changes is mandatory. Full stop.
Is there a possibility that keto makes exercise (which typically boosts bone health) harmful for your bones? Yes, but another possibility is that the changes researchers discovered during the study are not meaningful for long-term bone health.
In other words, the changes in CTX and other bone markers do not prove that keto causes bone loss in endurance athletes.
Length, Sample Size, and Demographics
Second, the study was short, with a small sample size.
Do the differences in bone markers even out over time? Do they become more dramatic? No one knows, because the study was 3.5 weeks, and it only included about thirty people.
And similarly, the bone health study would be more useful if the analysis controlled for age, gender, and other vital factors. While the study manuscript included gender, it didn’t include the age of participants, and it did not stratify results according to gender.
Body Weight and Spontaneous Weight Loss
Finally, although dietitians monitored the athletes in the study, the researchers did not report on changes in body weight.
And some research suggests hypocaloric (low-calorie) diets may increase CTX levels[*][*]. And not only that, but people often lose weight spontaneously by eating less when they go keto–such as in the 2019 keto military study.
Therefore, a possibility exists that the athletes in the low-carb group were undereating, and that insufficient calorie intake was the cause of their elevated CTX levels, as opposed to carb restriction per se.
Unfortunately, because the researchers either didn’t monitor or didn’t publish body weight changes, we have no way to know.
Currently, no substantial evidence exists that keto is harmful to your bone health.
A small 2017 study of children with epilepsy found that active children had lower bone mineral density on keto compared to less-active children[*].
However, strong evidence indicates that anti-epileptic drugs may decrease bone mineral density, which means that the 2017 study results may not apply to other groups of people, like adults without epilepsy[*].
And in contrast, numerous studies with hundreds of participants have shown no adverse bone health effects in adults and adolescents on the keto diet compared to other diets:
- Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet (Annals of Internal Medicine, 2010)
- Long-term effects of a very low carbohydrate weight loss diet and an isocaloric low-fat diet on bone health in obese adults (Nutrition Journal, 2016)
- Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: A 2-year non-randomized clinical trial (Frontiers in Endocrinology, 2019)
- Efficacy and safety of a high protein, low carbohydrate diet for weight loss in severely obese adolescents (Journal of Pediatrics, 2010)
In other words, if you’d prefer not to read dozens of pages of scientific articles, keto is safe and effective for weight loss and numerous other health benefits, and there’s no evidence it decreases bone mineral density.
Particularly for non-athletes, there’s no cause for concern.
But if you’re an endurance athlete and follow the keto lifestyle, or you just want to take extra precautions, keep reading!
Follow these tips to keep your bones in tip-top shape, whether or not you’re an endurance athlete.
To begin with, if you’re concerned about your bone health, don’t rely on guesswork. Instead, measure your bone mineral density yearly (or even twice yearly) using a DEXA (Dual Energy X-ray Absorptiometry) test[*].
Doctors recommend senior citizens get DEXA scans, but the test is also a great idea for athletes.
If your insurance doesn’t cover it, look for a good deal from “bone clinics” in your area. And as a bonus, you’ll also learn your lean body mass and body fat percentage.
Also, make sure you lift weights, especially if you’re an endurance athlete. But no matter who you are, resistance training is more effective than other forms of exercise for keeping your bone mineral density high as you age[*][*].
(Incidentally, another limitation of the 2020 Australian keto study was that participants only consumed around 16% of their calories from protein!)
Therefore, make sure to eat at least 25% of your calories from protein if you’re keto, but consider more if you are physically active.
Whey protein is one way to boost your protein intake, especially post-workout.
Finally, athletes who want the health and fat loss benefits of keto with the added performance benefits of carbs can use the targeted ketogenic diet (TKD) or cyclical ketogenic diet (CKD) to have the best of both worlds, as well as ensure their bones stay healthy while exercising.
Studies with hundreds of participants demonstrate that keto is safe and effective for fat loss and other health benefits, with no adverse effects on bone health.
However, we can’t draw conclusions about the effects of keto on bone mass in endurance athletes without better research.
Because the 2020 Australian keto study on bone health in race walkers didn’t measure bone mineral density, and because it was short with small sample sizes, reaching a firm conclusion isn’t possible.
Fortunately, if you’re on the keto diet, you can do plenty to build healthy bones: monitor your bone health, lift weights, eat plenty of protein, take collagen protein supplements, and consider TKD or CKD if you’re a keto athlete.