Given our obsession with dieting and weight loss, this subject strikes a chord with just about everyone. Weight is associated with bone mass. In general, a heavier person has higher bone density than a lighter weight person. Unfortunately, the relationship is not as simple as it seems.
When screening women for clinical trials, I thought that I could pretty well predict who was going to have low bone density by looking at their weight. After screening thousands of postmenopausal women with DXA scans for eligibility, I was astonished to find overweight and even obese women with low bone mass and osteoporosis.
What is most important to bone density is weight change or the fluctuations in your weight. Weight loss is beneficial for protecting against most health problems but it seems to be detrimental to bone health. That is the bad news!
DIETING: INTENTIONAL WEIGHT LOSS
Dieting that results in weight loss is associated with bone loss. Regaining weight does not necessarily increase bone mass. Yo-yo dieting, as well as sustained weight loss, can cause significant bone loss. Losing as little as one percent of your body weight may accelerate bone turnover.
Fighting midlife weight gain is a common battle. During the menopausal transition, along with all the hormonal changes, weight gain averages one pound a year. The Women's Healthy Lifestyle Project looked at dieting and exercise during this time period. They followed bone density changes across menopause in women with normal weight. Nearly four hundred perimenopausal women were randomly assigned to either a lifestyle intervention group or the control group, which had no intervention. The intervention focused on weight control, healthy diet, and exercise.
After the first year and a half, women in the lifestyle intervention group lost an average of seven pounds compared with women in the control group, who gained an average of one pound. Women in the intervention group also lost twice as much bone density at the hip as the women in the control group. Weight change was not related to changes in bone density at the spine.
At the end of four and a half years, the intervention group maintained a lower average weight than the control group, with a six pound difference. Hip bone density remained lower in the intervention group. Of note, the women who started on estrogen therapy in the transition did not lose as much bone mass. Spine bone density was similar in both groups.
Physical activity was primarily walking, which may not have provided enough high impact resistance to make a difference. The Women's Healthy Lifestyle Project proves that cutting back on calories and exercising works to fight weight gain but does not spare the bone, at least with walking as the sole exercise. Similar results have also been observed in premenopausal women who exercised while engaging in dieting that resulted in weight loss.
There is little information about the type or amount of exercise needed to balance the negative effects of weight loss on bone health. The exercise program might require more intensity, such as weight lifting (see the discussion of the BEST program in the section titled “Exercise: On Your Mark, Get Set, GO!”).
If you are dieting, be aware that you are at risk for bone loss. You will probably need a rigorous exercise program. Of course, you will also need adequate calcium and vitamin D supplements along with adequate dietary intake of protein to lose weight safely and, one hopes, to spare your bone.
If you are postmenopausal or in the menopause transition and have a history of weight loss due to sustained or yo-yo dieting, you should have an evaluation to measure your bone density with a DXA, along with a general risk assessment.
More clinical trials are needed in this area to determine exactly which exercises and other interventions will prevent bone loss during dieting. Further research on the mechanisms of dieting-induced bone loss may offer other strategies for prevention of bone loss.
UNINTENTIONAL WEIGHT LOSS ASSOCIATED WITH ILLNESS
In older adults, weight loss may be a marker for poor health. Bone loss associated with unintentional weight loss may parallel loss of muscle mass. With chronic or acute illnesses, there is a tendency toward unintentional weight loss, particularly among older adults. Physical limitations and immobility along with the underlying illness may contribute to bone loss and higher risk of falls and fractures. Bone loss and frailty due to weight loss with illness may compound the risk of hip fractures among individuals who are already at high risk.
WEIGHT LOSS SURGERY: GASTRIC BYPASS
Surgical therapy for obesity, termed “bariatric surgery,” has rapidly grown with the advent of new surgical techniques. Surgery using small incisions and an instrument with a camera on it, called a laparoscope, can be performed on an outpatient basis.
The gastric bypass surgery basically creates a smaller stomach, which limits food intake and leads to weight loss. The most common procedures reduce the size of the stomach either by placing a band around the stomach, the popular LAP-BAND®, or by stomach stapling.
A more extensive surgery, called “Roux-en-Y,” not only reduces the stomach size but also reroutes the intestine. The surgeon creates a small sac from the stomach that is connected to the middle portion of the small intestine. This results in the upper segment of the small intestine being bypassed. Some Rouxen-Y procedures may combine use of the stomach band with the intestinal bypass. As a result of the bypass of the upper portion of the small intestine, some essential nutrients are not absorbed, and some fat malabsorption also occurs.
This gastrointestinal “rearrangement” surgery creates a higher requirement for vitamin D and calcium because less area is available for absorption. “Restrictive” procedures that exclusively use banding or stapling are much less invasive because neither the stomach nor the intestine is cut. These procedures are less likely to create higher vitamin D and calcium requirements because the intestinal tract follows its normal course.
Multiple health benefits are derived from bariatric surgery. However, bone health may suffer. After gastric bypass surgery, there is a dramatic increase in bone turnover and bone loss. Studying a small group of patients who underwent the Roux-en-Y surgery, Mayo Clinic researchers found that 20 percent had fractured a bone within seven years of surgery. Their fracture rate was nearly double the expected fracture rate in a comparable group of people of similar age and sex.
Findings from another small series of patients treated at Columbia University with the Roux-en-Y procedure showed that bone density at the hip declined proportionally to weight loss. During the first year following surgery, the average weight loss was a hundred pounds. Bone density decreased by 8 percent at the total hip and was stable at the spine and forearm. The researchers found evidence of calcium and vitamin D malabsorption despite marked increases in calcium (100 percent) and vitamin D (260 percent) intake. Other studies have reported finding bone loss at both the hip and spine.
Awareness of bone health starts before gastric bypass surgery. Since vitamin D is stored in the fat, the more fat you have, the more vitamin D you need. Many patients are vitamin D deficient before surgery. Therefore, it is important to optimize vitamin D well before the surgery.
After surgery, it can be a challenge to provide enough calcium and vitamin D, as observed in published reports of patient cases. The type of surgery makes a difference in determining vitamin D and calcium requirements. Calcium is absorbed all along the small intestine. Most absorption occurs in the first two parts of the small intestine, called the duodenum and jejunum. Since the Rouxen-Y procedure connects the stomach directly to part of the jejunum, the opportunity for vitamin D and calcium absorption is greatly diminished.
Supplemental calcium and vitamin D are required. Those who have undergone a Roux-en-Y procedure may have difficulty maintaining adequate calcium and vitamin D. Therapy with portable light boxes that produce vitamin D in the skin is currently under investigation with patients who are unable to maintain sufficient levels with oral supplementation. Measurement of vitamin D levels will help guide the amount of supplements required to maintain vitamin D levels above 30 ng/ml. Other laboratory tests may be needed to monitor bone health status; these may include parathyroid hormone, serum calcium, serum phosphorus, and twenty-four-hour urine for calcium.
A DXA scan is recommended with a follow-up study in about two years. Fortunately, since most men and women who have gastric bypass start with high bone density, they do not typically reach osteoporosis levels even after significant bone loss. However, this loss may translate into higher than normal fracture rates.
If osteoporosis is found, an evaluation should investigate additional causes. Consideration for osteoporosis therapy should include other routes of delivery besides pills. These will include medicines administered by vein or by shots under the skin.
If you or a loved one has had gastric bypass surgery, assessment of bone health should be followed closely as part of the overall management plan.
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The Bare Bones
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