There are lots of upsides to losing weight, assuming you’re above your ideal body weight, but weight loss has a few downsides too if you don’t approach it properly. One thing you might not think about as the pounds drop off is the effect losing weight could have on your bones. One concern for all women, especially those over the age of 40, is maintaining a healthy bone density. In fact, one in two women and one in four men have a bone density that’s too low for health. That spells trouble since low bone density increases the risk for fractures, including hip fractures, the most serious kind.
The Impact of Losing Weight on Bone Density
Researchers at Washington University in St. Louis looked at the impact weight loss, with and without exercise, had on bone density. They divided 36 middle-aged, overweight men and women, average age 57, into three groups. To lose weight, one group cut their calorie intake by 20% and did no exercise. The other group lost weight by burning 20% more calories through exercise. A third group did neither. The good news is both the group that dieted and the group that exercised lost weight. In fact, the dieters lost more weight. The bad news is they lost bone mass too. That’s something few women (or men) can afford to lose.
What this study does point out is HOW you lose weight is important. The group that burned more calories through exercise lost weight and maintained bone mass. It was the group who lost weight through dieting who experienced a significant decrease in bone mass. This isn’t the first study to show dieting and calorie restriction without exercise boosts bone loss. Obese people who get bariatric surgery to lose weight often experience a reduction in bone density.
Some studies show obesity reduces the risk of bone loss after menopause. On the other hand, morbidly obese people may be at higher than expected risk for bone loss. Why this occurs isn’t clear. One theory is some obese people produce inflammatory proteins that activate cells called osteoclasts that break down bone tissue.
Why Does Dieting without Exercise Increase Bone Loss?
One way losing weight through calorie restriction may increase bone loss is through its effects on estrogen. Loss of body fat can lead to a reduction in how much estrogen your body is exposed to. Estrogen plays a vital role in bone formation and bone turnover. Bone tissue is constantly being broken down and replaced with new bone. Cells called osteoclasts break down old bone tissue and osteoblasts rebuild it. In the best of all possible worlds, osteoclasts and osteoblasts work together in a balanced manner so bone is replaced as it’s broken down. Lack of estrogen upsets this delicate balance and increases bone breakdown. Bone loss accelerates after menopause as estrogen levels drop.
Avoiding Bone Loss When You Lose Weight
Fortunately, as research shows, exercise helps prevent bone loss as a result of losing weight. High-impact exercise, where both feet leave the floor, helps preserve bone density by placing stress on the bone and forcing it to adapt to that stress. What’s less appreciated is the benefit resistance training has on bone density. When you train using a heavy resistance, 80% or more of your one-rep max, the muscle pulls on the tendon and the tendon pulls on the bone. This stimulates bone growth. Exercise is essential for all women who want to maintain bone density as they age but it’s even more important if you’re naturally thin, have small bones or are dieting to lose weight.
When you’re trying to lose weight and preserve bone mass, take a close look at the composition of your diet and make sure you’re getting enough protein. In one study, healthy, middle-aged people followed either a high-carbohydrate or a high-protein diet to lose weight. The participants also ate fruits and vegetables as part of their weight loss diet. Every four months for a year, while they were on the diets, researchers measured their bone density. While the high-carbohydrate group lost bone density, the high-protein group’s bone density remained stable.
At one time, it was thought that diets higher in protein might increase bone loss after it was found people on a high-protein diet had more calcium in their urine. It appears that the higher urine calcium reflects better calcium absorption rather than bone demineralization. Diets higher in protein in conjunction with adequate amounts of calcium seem to help with bone maintenance. Although the benefits of supplemental vitamin D for bone health are being questioned, it’s important to get enough of it so you’re not deficient. The best source is exposure to sunlight. Foods fortified with vitamin D, eggs and fatty fish contain modest amounts of vitamin D.
The Bottom Line?
When you lose a significant amount of weight, you can lose bone right along with it. Make sure you’re getting enough protein in your diet and that you’re doing some form of high-impact exercise and resistance training. Just as importantly, talk to your doctor about your risk factors for osteoporosis and when they recommend getting a bone density study.
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National Osteoporosis Foundation. “Exercise for Strong Bones”
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