Dec. 21, 2006  -- China announced plans Wednesday to tighten restrictions on adoptions by foreigners. The nation will give last priority to foreign citizens who are older than 50 and ban adoptions to those who are obese, single, disfigured or on antidepressant medication.

Stated bluntly, if you are too fat, you can't adopt a Chinese baby.

The laundry list of new restrictions on adoptions by foreigners is ostensibly aimed at assuring the babies a stable home conducive to good physical, mental and financial health. The changes are scheduled to take effect May 1, 2007, but already exert an influence.

This policy is misguided, discriminatory and shameful.

Admittedly, the new restrictions set the bar rather high for acceptable weight. Those with a body mass index above 40 will not be allowed to adopt. Overweight is defined as a BMI above 25; obesity is defined in three stages, beginning at a BMI of 30.

That said -- a woman 5 feet 4 inches tall is overweight at 145 pounds; stage 1 obese at 175 pounds; stage 2 obese at 205 pounds; and stage 3 obese at 230 pounds. No question, a BMI of 40 is quite high.

The policy would be worse, in practice, if the bar were set lower. But it's bad in principle as it is.

Preventing adoption based on weight, no matter what weight, only makes sense if there is evidence that parental BMI is legitimately linked to the quality of a child's life and health or the kind of parenting he or she receives. To my knowledge, that link doesn't exist

I've searched the medical literature for studies that link parental weight or BMI with quality of life in children and found nothing. I could find no studies that demonstrate a link between the BMI and the capacity to love. I found no system that correlates weight, waist circumference or any other measure of body size with the quality of parenting.

As for a link between parental weight and weight in their biological children, that's a well established fact in the medical literature: heavy parents are more likely to have heavy children. You barely even need to search the medical literature to make this case -- just look around. Kids tend to look like their parents.

The fact that kids tend to look like their parents in ways that have nothing to do with weight -- such as hair color and eye color -- is important. But I don't suppose the Chinese are worrying that if blue-eyed parents adopt Chinese babies, the babies' eye color will change.

The science clearly and consistently indicates that body shape and size in children resembles that of their biological parents for the same reason that eye color does -- because of genes.

There is no link -- repeat none -- between the weight of adults who were adopted as children and the weights of their adoptive parents, as has been confirmed by the famous decades-long Danish Adoption Study. More than 20 years of scientific studies have shown that nature, not nurture, explains the weight outcomes of adopted children.

Adopted children don't take on the body type or body weights of their adoptive parents. The science that supports that fact is not only persuasive, it is almost shocking. Virtually none of the variation in the BMI of adults who were adopted as children is explained by the weight of their adoptive parents, according to the research.

Of course, even if there was convincing evidence that the BMI of an adoptive parent did influence the health of a child, the list of restrictions imposed on adoption by the Chinese would be objectionable and arbitrary. There is no mention, for instance, of parental smoking. The link between smoking in a home and respiratory disease in a child is well studied and well established.

And while obesity is difficult to conceal -- so a potential adoptive parent could never lie about their weight -- everything from drug use to anorexia nervosa to hepatitis is potentially invisible. Singling out obesity as a measure of health just because it happens to be detectable is neither rational, nor fair.

Of course, if the Chinese are worried about obesity affecting babies, they should probably ban adoption by Americans altogether. Many studies show that coming to the United States to live is a major obesity risk factor. And if the adoption policies are about health, then parental dietary and physical activity patterns might be worth assessing, as these are apt to influence the well-being of a child. It is certainly possible to be thin and very unhealthy.

The biggest reason China is imposing restrictions on adoption is because it can, I suppose. A lot of foreigners are trying to adopt Chinese babies, and the government can afford to set limits. There are far more non-Chinese adults wanting to adopt than there are Chinese babies available. In the crudest of terms, it is a sellers market.

The Chinese presumably could, if they wanted to, require that applicants be able to juggle or knit or play the piano. If their intent is to create arbitrary barriers so that the mismatch between supply and demand is resolved, these would work just fine.

If their intent is to ensure babies a nurturing and loving home, however, these restrictions would be ridiculous.

So is the notion that you can measure the quality of a parent on a bathroom scale.