Could eating a keto or LCHF diet harm bone health?
, medical review by Dr. Bret Scher, MD
in Keto, Low carb & high fat 
Keto diets have been shown to provide a number of health benefits, including helping people lose weight, control blood sugar, and reduce heart disease risk factors. But could following a keto way of eating be bad for your bones? A recently published study seems to hint that it might:
In this trial, 30 world-class race-walkers chose to follow either a high-carb, low-fat diet or a low-carb, high-fat (LCHF) keto diet for 3.5 weeks. Both diets were high in protein and contained enough calories to meet the individualized needs of each athlete. At the end of the study, several markers of bone metabolism were measured.
According to the researchers, the keto diet increased markers of bone breakdown and decreased markers of new bone formation. Once people in the keto group added carbs back to their diet, some of these markers recovered, whereas others remained altered. The authors concluded that keto diets might have detrimental effects on bone health and that further long-term studies are warranted.
This may sound concerning to those of us who follow a keto or LCHF way of eating. However, there are a few things to consider here.
First, what do the changes in these markers mean for bone health in the long term? We really don’t know. Might they have improved on their own after a period of keto-adaptation, which can take months? A study lasting less than 4 weeks simply can’t predict what might happen months or years later. We’d need DEXA scans and other information to assess whether there was any connection between eating low carb and bone loss or other problems.
Secondly, this was a study of elite athletes, so responses may differ among those of us who fall outside of that group.
Finally, the authors’ recommendation for further studies on the long-term effects of low-carb diets on bone health seem to make sense. Yet there are already several longer high-quality trials with DEXA scans and other data that show no detrimental effects of ketogenic diets on bones.
At Diet Doctor, we take all of the evidence into consideration rather than relying on the most recent study making headlines. So since we have significantly more reliable data to the contrary, a 3.5-week study like this isn’t enough to sway our position.
Earlier
New JAMA article discusses benefits of keto diet but warns it may be risky long term
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For instance, a lot of carby foods have copper, whose deficiency is one cause of osteoporosis.
There are plenty of keto foods that have copper, but people are not aware of it.
Now, we all know that low carb diets INCREASE requirements for minerals like Sodium, Potassium, and Magnesium. So does exercise.
Basically the Low Carb athletes in this study received less Potassium, Magnesium, Calcium, Phosphorus, Iron, and Zinc (and possibly sodium but we don’t know) than the other 2 groups they were being compared with. The Low carb athletes intake of potassium did not even met the adequate intake specified by the National Health and Medical Research Council. (See table 4, Mirtschin 2018).
The low carb athletes probably all had keto flu due to low electrolytes and so little time to adapt to the diet.
“Micronutrient intakes and micronutrient density (per MJ energy) were similar in the HCHO and PCHO diets; however, values were consistently lower for the LCHF diet.” (Mirtschin 2018)
“The mean potassium content of the LCHF diet was slightly less than the adequate intake (National Health and Medical Research Council, 2006), perhaps justifying the recommendations to consume electrolyte supplements while following this dietary philosophy (Volek & Phinney, 2012).” (Mirtschin 2018)
Sodium was not measured. “The use of low - and noncaloric condiments (salt, pepper, spices, etc.) was encouraged to allow flavoring of meals but was not recorded due to the inability to track their minimal weight“(Mirtschin 2018)
How on earth could a low carb diet high in red meat be lower in iron?
Low carb dieticians usually manage to exceed dietary recommendations for micronutrients with a low carb diet. However, portion size, and preparation methods are very important. Slicing and boiling meat can remove many essential minerals, as Volek & Phinney (2011 p151) noted about the Yale Turkey Study (DeHaven 1980). Simply boiling the meat and throwing out the minerals in the water can destroy sodium balance. How the meat was prepared in this study is not reported, nor are the amounts consumed.
So what do we know?
The low carb athletes got electrolyte OR diet cola drinks ONLY 2 days a week in the morning. The other athletes got sports drinks/gels 6 days a week (or lollipops Wednesday & Saturday) in the mornings.
In the afternoon the low carb athletes received electrolyte drinks, and the others got sports drinks.
Which electrolyte drinks, diet cola, sports drinks, gels and lollipops were used is not specified.
Diet cola is not exactly high in all required electrolytes, nor is it good for bones. For example: Diet Coke contains phosphoric acid, and potassium benzoate. Coke Zero & Coke Zero Sugar contain phosphoric acid, and potassium as potassium benzoate, potassium citrate & acesulfame potassium.
None of these diet drinks contains the required sodium or magnesium.
Phosphoric acid is associated with osteoporosis.
Bone broth was NOT offered. Greens high in magnesium like kale & spinach probably were not offered – there are references to lettuce, cucumber, Avocado, Cauliflower, Green salad & zucchini. Presumably the green salads used lettuce.
No estimate of vitamin K2 intake.
The study was run over only 3.5 weeks.
Although the diets are reported in better detail than is usual for a nutrition journal, there is not enough detail for the experiment to be accurately repeated, which should be a basic requirement for publication.
They only looked at markers of bone health, not bone density, over a very short period of time.
There was no report specifically on cramps, but 2 participants were excluded from the 10km race because of soreness or injury, one probably from the low carb group. (Burke 2017).
In the walking trial of 10km & 25 km it was claimed that “adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity.” (Burke 2017) The maximum time required was ≤ 2 hours, so it was not really an endurance test. Low carb is probably not best for sprints and medium distance events, but should be better for fuelling long distance events where participants are likely to exhaust glycogen stores and bonk before completion. Plus the low carb athletes probably had the keto flu from low electrolytes and the newness of the diet.
To understand the study at least 3 papers need to read:
The walking trial (Burke 2017): https://doi.org/10.1113/JP273230
The Diet (Mirtschin 2018): https://doi.org/10.1123/ijsnem.2017-0249
Bone Health (Heikura 2020): https://doi.org/10.3389/fendo.2019.00880
Also:
Volek & Phinney 2011: https://lowcarbdownunder.com.au/.../the-art-and-science.../
DeHaven 1980: https://doi.org/10.1056/NEJM198002283020901
Louise Burke: https://scholar.google.com.au/citations?user=dAoAR6sAAAAJ...
While one wonders what would have happened if the low carb athletes had received more electrolytes, the article does raise a very important point:
People on a low carb diet need to WATCH THEIR ELECTROLYTE CONSUMPTION!
(to avoid keto flu, cramps, and possibly
...and magnesium! Sorry, I had that other post queued up when I replied. It wasn't a reply directly to you.