In 2005, Frank Hu and JoAnn Manson (Harvard) published a study in the JAMA "proving" that an overweight person cannot be physically fit even if they regularly exercise.  This was an epidemiological study (notoriously inaccurate), using an already existing data set.  In this cohort of 170 women, those who had a BMI of 30 to 40 (obese to clinically obese) had an increased risk of 1.69 (not significant). For those with a BMI over 40, the increased risk was slightly over 2.  Since their exercise habits were only collected 5 times since 1976 (long before cardio was known to be healthy), and since people in the obese to clinically obese BMI range tend to weight cycle, a practice known to raise the risk factor, in looking at the study one can easily see the flaws. In short, the risk factor for 11,000 women was decided from the limited data on 170 women!  Both Willet and Manson admitted connections with either the diet industry and/or the pharmaceutical industry. Here is a detailed analysis of the flaws of this study.

Happily, we have updated information on this.  In July 2010, NPR ran an article about the research of Cardiologist C. Noel Bairey-Merz.  She did a metastudy and concluded that "fitness" trumps "fatness".  Dr Bairey-Merz is the director of the Women's Heart Center as well as the Preventive and Rehabilitative Cardiac Center at Cedars-Sinai Heart Institute.

She stated:

>>>those who are fit are people who could walk 30 to 60 minutes without having to stop; who could climb two flights of stairs without becoming winded; or who could do some mild to moderate aerobic activity — a brisk walk or short jog, for example.<<<

And she found that exercise helped everyone:

>>Such routine exercise strengthens heart and lung function, bones and muscles, as well as how the body processes oxygen. The greater the efficiency of these functions, the greater one's fitness.<<

Dr Bairey-Merz concluded that women who regularly exercise are under less risk than those who do not, regardless of size, a result found by the large Cooper Institute studies also. She further commented that her research found that a few extra pounds may be beneficial for folks - studies have suggested that folks in emergency care who are a bit overweight, tend to have a higher survival rate than those in the "perfect weight" BMI range.