Obesity Paradox #9 — Fat on the brain

The media’s not too keen on reporting studies that might give people the idea that body fat is normal and might actually be healthy. The natural weight gain that comes with aging seems especially “bad news,” even though the weight of evidence continues to support that having body fat reserves is a survival advantage.

As we get on in years, however, cognitive decline is one of the most feared conditions. Dementia is incapacitating and leads to functional decline and can devastate the quality of life for its victims and their families. So, it is especially puzzling why the news isn’t all over studies offering insights that could lead to answers for millions of adults, and lessen concerns with risky dieting and trying to achieve thinness in retirement age.

Research led by Dr. Maureen T. Sturman, M.D., MPH, at the Rush Institute for Healthy Aging, set out to find the relationship between obesity among seniors and cognitive decline. The results were not what the researchers appear to have expected.

They used information on 3,885 Black and Caucasian participants in the Chicago Health and Aging Project, which followed seniors living in the community in the south side of Chicago from 1993 to 2003. Every three years, the seniors were interviewed, medical histories taken, and cognitive assessments done, using four tests (Mini-Mental State Examination, the East Boston Tests of Immediate Memory and Delayed Recall; and the Symbol Digit Modalities Test). Dr. Sturman’s team found a significant relationship between underweight and cognitive decline over time. In comparison, there was lower cognitive decline among overweight and obese people, with each increase in BMI associated with less cognitive decline.

They then reanalyzed the data using several different modelings and were unable to remove the favorable associations between higher weights and preservation of cognitive function. They further adjusted for illnesses, including heart disease, stroke, diabetes, hypertension, and still the association didn’t change substantially. Finally, they eliminated 1,010 of the participants from their analysis to exclude those with low scores on one of the tests (MMSE) and only then were able to make the associations between BMI and cognitive decline statistically not significant.

So what did they conclude? “The findings suggest that greater body mass index in old age is not predictive of cognitive decline in a cognitively unimpaired community population.”

Now, we all know that a single study does not make for scientific truth. Nuggets of information build a body of evidence, which is why Junkfood Science tries to focus on studies that challenge us to think and that support the strongest body of evidence — especially when it’s the stuff we rarely hear.

The discussion section in this study noted that their findings were consistent with a growing body of evidence showing low BMI, and weight loss, in seniors is associated with, and often precedes, mental decline. This study is also consistent with others showing that high BMIs are associated with better cognitive functioning and less cognitive decline among both Blacks and Caucasians.

For example, researchers at the Rush Alzheimer’s Disease Center and Rush University Medical Center in Chicago, studied 918 senior clergy in the Religious Orders Study who had no signs of dementia at the beginning of the study. After following these seniors for nearly 6 years, they found a significant association between low BMIs and declining BMIs and the development of Alzheimers. For every 1 unit of BMI less at the start of the study, there was a 5% increased risk; but every 1 unit decline in BMI during the study was associated with a 35% increased risk for Alzheimers per year. These relationships held after controlling for chronic diseases and even excluding those who developed Alzheimers during the first 4 years.

These studies are observational, so can’t prove causation, but they do lead to a number of reasoned, plausible physiological mechanisms which may explain the protective function of fatness in mental function. Nutritional status is one, which has been well covered already. We’ve also seen how many of the slightly higher health risk indices associated with higher weights and aging aren’t actually proving to predict health problems and premature deaths. The research examining these “paradoxes” were discussed by the Rush Center researchers. “An increased BMI appears to increase cardiac output and stroke volume which may enhance cerebral blood flow and improve cognition,” they wrote. Higher blood levels of insulin growth factor has also been shown to be “associated with both improved cognition and a slower rate of cognitive decline."

Which leads us to another study in a September issue of the journal Neurology. It reported the results of the Leiden 85-Plus Study of 599 seniors who’d been assessed every year from age 85 using four neuropsychological tests. It found that those with hypertension, obesity, high cholesterol and higher blood sugar levels — nicknamed “the metabolic syndrome” — had less cognitive decline than those with “good” numbers. The protective indices appeared to primarily be higher blood sugars, higher body weights and higher blood pressure.

There is considerable evidence, they wrote, that in very old people, low blood pressure, low cholesterol and low weight or weight loss are associated with increased risk of dementia and higher mortality rates.

In other words, the idea that we should all have identical health risk indices (“numbers”) throughout our lives is unsupported. They concluded that the metabolic syndrome appears invalid in aged seniors. That would mean that the appropriateness of treating these health indices in this age group might best be reevaluated.

Fat is associated with mental sharpness. Yet, pop culture believes that fat people have emotional or mental problems. Many fat people are told and become convinced they have “issues” with food, under the myth that eating causes obesity when, in fact, fat and thin people eat no differently to explain the natural diversity of sizes. Also widespread among pop science is the belief that fat people are miserable, depressed and suicidal. “Excess weight is our heavy, unhappy thoughts about ourselves, or our uneasy lives, projected outwardly,” said the author of the “non-diet” diet book, Soul-Full Eating. She said that by eating pure, “light-filled” natural foods containing “vital earth energy” and eating “mindfully,” we can all maintain an “ideal” weight. That’s a myth, too.

That brings us to a myth-busting study in the March issue of Archives of Internal Medicine. Led by Dr. Kenneth J. Mukamal, M.D., MPH, at Israel Deaconess Medical Center, the Boston researchers analyzed the Health Professionals Follow-up Study participants. They used a cohort of 46,755 male medical professionals, ages 40 to 75, who were cancer free. Biannually from 1986 to 2002, the men had completed questionnaires reporting their body measurements, lifestyle factors, physical activity, a food frequency questionnaire and quality of life measures. Deaths were confirmed and the researchers reviewed the death certificates, hospital and pathology reports to determine the causes of death for those who died. During the study, 131 men had committed suicide, at an average age of 64. This suicide rate was similar to other large cohort studies, they noted.

Most striking was the finding of a steady and dramatic stepwise decrease in the risk of suicide — a four-fold gradient in risk even after adjusting for confounding factors — with rising BMIs at baseline. Suicide risk dropped by 11% for every 1 unit increase in BMI among the men.

This significant effect was not influenced by disease or social support, marital status, work status, or any specific foods. They specifically noted, for instance: “Although carbohydrate intake in particular has been postulated to improve mood and increase weight, glycemic load had no effect on our estimates of risk.” They tried analyzing the data by excluding all of the men with BMIs under 21, but the risk trajectory held. They even excluded all men who lost weight to minimize the contribution of weight loss before suicide. [Large amounts of weight loss within 2 years was associated with a higher risk, but wasn’t statistically significant.] Defusing another blame behavior, they found that lesser physical activity (MET-hours/week) was associated with lower the risk. The heaviest men had the highest rates of diabetes and hypertension, but the lowest suicide rates. Even being fat when younger was examined and men who were overweight at age 21 had the lowest risks. Although they didn’t specifically assess depression, antidepressants increased suicide risk 6-fold, which would indicate men with lower BMIs were more depressed.

In reviewing the body of evidence to date, Dr. Mukamal and colleagues found most of the strongest studies found similar associations. In fact, they noted that “increased prevalence of overweight and obesity in the United States in the 1990s was accompanied by a 6% decrease in suicide mortality rates.” Several studies have suggested that “the stigma attached to obesity may be particularly acute among women,” leading to more depression, but this hasn’t consistently been born out in studies, they said. Interestingly, they noted that because of the changes in muscle mass in older adults, (muscle is used popularly used to explain away higher BMIs in younger men), it lends further support for “the importance of adiposity per se in lowering the risk of suicide.”

Letters in the current issue of Archives of Internal Medicine, discussed this study. Italian researchers wrote of research suggesting that lower levels of blood cholesterol may explain the relationship between low BMI and suicidal behavior. And doctors at the University of California-San Diego wrote of their research from the Helsinki Heart Study corroborating its findings. They found that markers of insulin resistance, including higher BMIs, are linked to reduced risks of suicide possibly because of the higher free fatty acids associated with insulin resistance, which portends higher serotonin levels.

What is striking about all of this research, besides the fact it didn’t make the news and isn’t common knowledge, is that no matter how hard some researchers are trying to find reasons why the natural weight gain that comes with aging is bad for us, and how much they torture the data, they can’t. Maybe, Mother Nature isn’t so dumb after all with the natural creeping up of weights and health indices as we age.

© 2007 Sandy Szwarc

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