Physiology Friday #136: Does Time-restricted Eating Negatively Impact Bone Health?
A short eating window may help you drop weight while maintaining a strong skeleton.
Welcome to Physiology Friday.
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Quick finding of the week: Exercise longer (and harder) for cardiovascular health? A study of over 88,000 adults found that more physical activity was associated with a reduced risk for cardiovascular diseases including ischemic heart disease and cerebrovascular disease. However, those who achieved more moderate to vigorous activity experienced a greater risk reduction — around 14% lower in people for whom intense activity made up a greater percentage of their total weekly physical activity energy expenditure.
Tl;dr; those who exercised the most and at a higher intensity experienced the lowest risk for cardiovascular diseases.
Fasting, weight loss, and bone health
Weight loss is a contentious topic. While there are nearly infinite ways to go about shedding extra pounds using diet, exercise, or other lifestyle strategies, nobody can agree on which practice is best. Adherence to traditional dietary and exercise advice typically tends to be abhorrently low, and studies that do report weight loss using these approaches are often short in duration, leaving us to wonder whether the participants maintained their weight loss in the long term.
As far as “novel” approaches to weight loss go, time-restricted eating (TRE) is perhaps the one most in the public eye. There’s seemingly a new TRE study published each week (if you read this newsletter consistently, you’re already well aware of this).
Why is TRE so popular, both as a weight-loss method and a practice for those looking to improve metabolic health and body composition? TRE appears to have many advantages compared to conventional caloric restriction. For one, it’s more sustainable (for some people), easy to implement (for some people), and tends to decrease rather than increase hunger (in some people). You’ll notice my liberal use of “for some people,” and the reason for this is that TRE is not the “magic pill” for everyone. I hate to use blanket statements that make it seem like every diet or exercise routine works for all people. That’s rarely, if ever, the case. But I digress.
There may be another unique benefit to TRE when it comes to weight loss.
In some longer-term studies, weight loss achieved through conventional caloric restriction has caused bone loss, decreased bone mineral density and bone mineral content, and even increased the risk of fractures in some populations. This obviously isn’t a desirable outcome, even if one is sacrificing bone health for improved metabolic health.
In that regard, it would be prudent to determine whether TRE-induced weight loss may have the same effects on bone health as that shown for caloric restriction. Some studies have indicated that 6 or 12 weeks of TRE doesn’t negatively impact bone health markers, but it’s unknown if a longer-lasting TRE intervention would have similar effects.
In a new study published in the journal Obesity,42 adults with overweight or obesity were randomized to complete 6 months of 12-hour TRE or were assigned to a “control” intervention in which they received a short nutritional counseling session. Other than the strict eating window for the TRE group and the dietary advice provided to the control group, there were no instructions for participants on what or how much to eat.
The researchers measured participants’ bone mineral density and bone mineral content at the start and finish of the 6-month study. A marker of bone breakdown called CTX and a marker of bone formation called P1NP were also measured before and after the intervention, in addition to vitamin D levels, parathyroid hormone levels, and a growth factor known as insulin-like growth factor-1 (IGF-1).
Among all of the participants, there were no changes within the TRE or the control group for bone mineral density, bone mineral content, markers of bone breakdown or bone formation, and blood biomarkers.
But then the researchers divided participants into categories based on their level of weight loss during the study: those who were considered “weight loss responders” and lost more than 0.6 kilograms (1.3 lb) during the study, and those who were considered “weight loss non-responders” and lost less than 0.6 kg (1.3 lb) during the study.
For the participants in the TRE group who were weight loss responders, CTX levels decreased during the study, while CTX levels increased in the control group. In other words, TRE seemed to prevent bone breakdown during weight loss, while markers of bone breakdown were elevated in the control group participants who lost weight. Markers of bone formation were unchanged in the TRE and control groups.
Bone mineral content decreased in the control group weight loss responders but didn’t change in the TRE group, while bone mineral density didn’t change in either group.
There were no changes in vitamin D, parathyroid hormone, or IGF-1 in any group.
The authors interpret these findings as TRE having a “bone-sparing” effect during weight loss. And indeed, the participants who achieved weight loss during the TRE intervention were protected from some of the effects that the control group experienced during weight loss — including a loss of bone mineral content and an increase in markers of bone breakdown.
Now, some of the differences were small, and a 6-month study is still somewhat short for the measurement of an outcome like bone health. It may not tell us much about how years of TRE might impact the health of our bones or increase the risk for osteoporosis.
Nonetheless, this study does complement the other controlled trials on TRE that haven’t observed adverse effects of this dietary strategy on bone health. So overall, the evidence seems to suggest that TRE is not only effective for improving metabolic health and promoting weight loss, but it’s safe for bone health in adults.
Of course, studies in older adults or people at risk for bone-health-related conditions may experience different effects than the healthy population included in this study. But for those who may have had qualms about adopting TRE for bone-related concerns, here’s at least one data point to ease the hesitation.
Thanks for reading. See you next Friday.