I'll note so-called overweight - BMI 25-30 - is the longest-lived cohort, followed by normal (18-25), obese (30-40), underweight (<18), morbidly obese (40+).
Professors Frank B Hu and Walter Willett of the Department of Nutrition, Harvard School of Public Health, wrote in a letter to the editor in 2000, in the American Journal of Clinical Nutrition, that the China-Cornell-Oxford Project did not find a clear association between animal-product consumption and heart disease or major cancers, although in 2010, in an article, "Healthy eating guide," Willet encouraged people to choose plant-based proteins over animal sources.[30] Willett is the principal investigator of the "Nurses' Health Study II" (established 1989). Campbell is highly critical of the first Nurses' Health Study (established 1976), calling it one of the chief sources of public misinformation about nutrition.[8]
In a written debate with Campbell in 2008, Dr. Loren Cordain, a professor in the Department of Health and Exercise Science at Colorado State University, argued that "the fundamental logic underlying Colin's hypothesis (that low protein diets improve human health) is untenable and inconsistent with the evolution of our own species," and that "a large body of experimental evidence now demonstrates a higher intake of lean animal protein reduces the risk for gout, cardiovascular disease, hypertension, dyslipidemia, obesity, insulin resistance, and osteoporosis while not impairing kidney function." Campbell responded by questioning the implications of the evidence Cordain noted, and argued that "diet-disease associations observed in contemporary times are far more meaningful than what might have occurred during evolutionary times—at least since the last 2.5 million years or so."[31] Cordain's rebuttal countered that contemporary hypothesis regarding "what modern day humans should and shouldn’t eat must be consistent with the system and the ancient environmental selective pressures that engineered our current genes," and that "there is no credible fossil, archeological, anthropological, anatomical, ethnographic or biochemical evidence to show that members of our genus (Homo) routinely consumed low protein diets. In fact, without the inclusion of energetically dense animal food into the hominin diet, starting at least 2.5 million years ago, our large energetically active brains would not have evolved."