By Jay Cao

Obesity and osteoporosis are public health problems.

Obesity is a condition where excessive fat accumulates to a state that poses risks to health — it is largely due to an imbalance of calorie consumption and expenditure. The problem is growing in prevalence among all age groups, especially people in rural areas where income is below average.

Osteoporosis is a disease condition in which bones become spongy and are easily broken. With aging, and changes in lifestyle, more bone structure is broken down than is rebuilt. Many factors can contribute to osteoporosis development, such as reduced physical activity, decreased ability to absorb nutrients, increased use of medications such as glucocorticoids and a sudden decline in the female hormone, estrogen, in menopausal women.

Obesity: Bad for bones?

Many scientific studies have made it clear that obesity is a risk factor for many chronic health problems, such as coronary heart disease, type 2 diabetes, high blood pressure, osteoarthritis, depression, gall bladder disease, cataracts and certain types of cancers.

In terms of bone health, it used to be thought that because obese people are heavier, they must have stronger bones to support such weight and, therefore, are less likely to have osteoporosis. The mechanical loading of body weight is good for bones so, in general, it is true that the more a person weighs, the stronger the bones are. But it is incorrect to think the body weight as the form of fat mass would have the same effect on bone as lean muscle. Actually, it has been demonstrated that fat mass is negatively associated with bone mass when the mechanical loading effect of body weight on bone mass was accounted for.

Data published in recent years have come to clarify this discrepancy, that is, having excess fat mass or being obese is bad for bone mass and strength in children, adolescents and adults. Extra fat mass during both childhood and adolescent stages can harm bone material and strength. It also increases the risk of osteoporotic fracture later in life.

Greater the fat mass is associated with lower bone density in hip, lumbar spine and total body in postmenopausal women, compared with lean individuals having the same weight. Finally, high fat intake can cause the formation of insoluble calcium soaps in the intestine and, therefore, reduce absorption of calcium, an essential mineral for bone.

Furthermore, fat tissue is not an inactive bystander in the body or just for energy storage as people have commonly thought. Fat tissue can secrete many active signal molecules called inflammatory cytokines. It is these cytokines that cause health problems that we have seen in obesity. These same signal molecules also have been found to increase the activity of cells that break down bones.

Other evidence supporting the direct relationship between obesity and osteoporosis includes:

• Bone-forming cells and fat cells formed from the same stem cells. In other words, the more bone forming cells produced, the fewer fat cells are made.
  
• Aging and menopause are associated with bone loss as well as fat mass buildup.
  
• Physical activity reduces fat mass while increasing bone mineral density and strength.
  
• Chronic use of steroid hormone increases the chance of becoming obese and causes bone loss.

Prevention

The good new is that obesity is preventable, and so is osteoporosis. Reducing calorie intake and increasing calorie expenditure help you lose fat mass and achieve a healthy body weight. Consuming adequate nutrients such as calcium, vitamin D, magnesium, zinc and protein helps support bone health. Exercise is a useful way to increase energy expenditure, and it is also an effective way to prevent or reduce the incidence of osteoporosis.

Many small steps can help you achieve healthy body weight and build better bones. Here are few tips:

• Drink water before a meal, use fat-free milk instead of whole milk, and don’t eat late at night.
  
• Eat lean red meat and poultry; eat more fruits and vegetables, eat smaller desserts, and eat off smaller plates to help you eat smaller portions.
  
• Exercise at least 30 minutes on most days of the week, walk instead of drive, and take stairs instead of elevators. You will be going in the right direction to reduce body fat and strengthen bones by being physically active.

For more information on diet and physical activity, go to the U.S. Department of Agriculture sponsored Web site www.mypyramid.gov.

The most important thing is to start today one step at a time!

	ARS News & Events Links   ARS News & Events   Agricultural Research Magazine   Image Gallery