It can seem like a cruel contradiction: lose weight, lose bone mass. Lose a lot of weight and lose even more. (Rest assured there’s more to the story, but we continue….) A collaborative study involving researchers from the University of Kansas and the University of Missouri highlights the downside of weight loss by calorie restriction both during and in the months following weight loss.
Researchers examined protein markers of bone breakdown and formation in 37 obese, middle-aged adults who lost 20 percent of their body weight through a severe calorie-restricted diet. Protein markers, which are released during bone breakdown and formation, are used as indirect indicators of bone remodeling. During the 3-month weight-loss phase, bone remodeling was elevated, and bone formation and breakdown were imbalanced as a result of a low energy intake. After weight loss phase, bone remodeling remained elevated during the 9-month weight maintenance phase, but bone formation and breakdown appeared to be balanced.
via Science Daily 
Though the bone breakdown and formation rate had hit a homeostasis, the researchers caution that “Rapid rates of bone remodeling, regardless of the balance of breakdown and formation, can increase bone fragility.” They add that those seeking to lose weight should consider adding weight-bearing exercise and make sure they’re getting adequate calcium.
Our reaction? Well, yeah. Weight-bearing exercise is absolutely essential for maintaining not just muscle mass but bone density. Bone density is not only influenced by how much weight the body senses it carried around but how much “work” the body senses is happening in the bone and muscle connections. Countless studies have confirmed this, and research out of Washington University School of Medicine in St. Louis highlights its “osteoprotective effect” in weight loss. Their study  compared bone density (as measured by blood markers and dual-energy x-ray absorptiometry) in two groups of older adults, one of which lost weight through restricting calories and the other by exercise. Their results? Though the CR group lost some 2.2 % of bone density in fracture-prone areas like the lower spine, pelvis and femur, the exercise group showed no substantial change in bone density. Though both groups showed higher rates of bone turnover than the control group, the researchers indicated  that the work of exercise, the “muscles pulling on bones” can “produce strains in the skeleton that stimulate new bone production.” The “exercise-induced mechanical strain,” they say is actually healthy and protective.
The Primal Blueprint isn’t about caloric restriction. Interestingly though, when people cut out the carbs, they’re surprised how much their calorie intake drops. (The same is true for lab animals: caloric restriction diets generally reduce carb calories more than any other macronutrient.) But it’s ultimately about how your diet complements your body’s natural functioning. As Mark has said in the past, the “success” of CR in weight loss probably has more to do with insulin mitigation than with sheer calorie reduction. Add to this picture an exercise routine that challenges the body’s physical structure and fitness in a natural, optimal way, and you’re going to see optimal health. And wouldn’t you know it? That includes bone health.
Thoughts? We’d love to hear your questions or additions to what these studies highlight.