Tag Archives: weight loss

Fat people live longer, show less dementia

Life expectancy is hardly affected by weight in the normal - overweight- obese range. BMI 30-34.9 = obese.

Life expectancy is hardly affected by weight in the normal – overweight – obese range. BMI 30-34.9 = obese.

Lets imagine you are a 5’10” man and you weigh 140 lbs. In that case, you have a BMI of 20, and you probably think you’re pretty healthy, or perhaps you think you’re a bit overweight. Our institutes of health will say that you are an “average-wight” or “normal-weight” American, and then claim that the average-weight American is overweight. What they don’t tell you, is that low weight, and so-called average weight people in the US live shorter lives. Other things being equal, the morbidity (chance of death) for a thin American, BMI 18.5 is nearly triple that of someone who’s obese, BMI 32. The morbidity of the normal-weight American is better, but is still nearly double that of the obese fellow whose BMI is 32.

Our NIH has created a crisis of overweight Americans, that is not based on health. They work hard to solve this obesity crisis by telling people to jog to work, and by creating ever-more complicated food pyramids. Those who listen live shorter lives. A prime example is Jim Fixx, author of several running books including “The complete Book of Running.” He was 52 when he died of a heart attack while running. Similar to this is the diet-expert, Adelle Davis, author of “Let’s eat right to keep fit”. She died at 70 of cancer — somewhat younger than the average American woman. She attributed her cancer to having eaten junk food as a youth. I would attribute it to being thin. Not only do thin people live shorter lives, but their chances of recovering from cancer, or living with it, seem to improve if you start with some fat.

The same patter exists where age-related dementia is concerned. If you divide the population into quartiles of weight, the heaviest has the least likelihood of dementia, the second heaviest has the second-least, the third has the third-least, and the lightest Americans have the highest likelihood of dementia. Here are two studies to that effect, “Association between late-life body mass index and dementia”, The Kame Project, Neurology. 2009 May 19; 72(20): 1741–1746. And “BMI and risk of dementia in two million people over two decades: a retrospective cohort study” The Lancet, Volume 3, No. 6, p431–436, June 2015.

Morbidity and weight, uncorrected data, and corrected by removing the demented.

Morbidity and weight, uncorrected data, and corrected by removing the demented. The likelihood of dementia decreases with weight.

Now you may think that there is a confounding, cause and effect here: that crazy old people don’t live as long. You’d be right there, crazy people don’t live as long. Still, if you correct the BMI-mortality data to remove those with dementia, you still find that in terms of life-span, for men and women, it pays to be overweight or obese but not morbidly so. The study concludes as follows: “Weight loss was related to a higher mortality risk (HR = 1.5; 95% CI: 1.2,1.9) but this association was attenuated when persons with short follow-up or persons with dementia were excluded.” As advice to those who are planning a weight loss program, you might go crazy and reduce your life-span a lot, but if you don’t go crazy, you’re only reducing your life-span a little.

In terms of health food, I’ve noticed that many non-health foods, like alcohol and chocolate are associated with longevity and mental health. And while low-impact exercise helps increase life-span, that exercise is only minimally associated with weight loss. Mostly weight loss involves changing the amount you eat and changing your clothes choices to maximize radiant heat loss.

Dr. Robert E. Buxbaum, October 26, 2017. A joke: Last week I was mugged by a vegan. You may ask how I know it was a vegan. He told be before running off with my wallet.

Most Heat Loss Is Black-Body Radiation

In a previous post I used statistical mechanics to show how you’d calculate the thermal conductivity of any gas and showed why the insulating power of the best normal insulating materials was usually identical to ambient air. That analysis only considered the motion of molecules and not of photons (black-body radiation) and thus under-predicted heat transfer in most circumstances. Though black body radiation is often ignored in chemical engineering calculations, it is often the major heat transfer mechanism, even at modest temperatures.

One can show from quantum mechanics that the radiative heat transfer between two surfaces of temperature T and To is proportional to the difference of the fourth power of the two temperatures in absolute (Kelvin) scale.

P_{\rm net}=A\sigma \varepsilon \left( T^4 - T_0^4 \right).  Here Pnet is the net heat transfer rate, A is the area of the surfaces, σ is the Stefan–Boltzmann constantε is the surface emissivity, a number that is 1 for most non-metals and .3 for stainless steel.  For A measured in m2σ = 5.67×10−8 W m−2 K−4.

Unlike with conduction, heat transfer does not depend on the distances between the surfaces but only on the temperature and the infra-red (IR) reflectivity. This is different from normal reflectivity as seen in the below infra-red photo of a lightly dressed person standing in a normal room. The fellow has a black plastic bag on his arm, but you can hardly see it here, as it hardly affects heat loss. His clothes, don’t do much either, but his hair and eyeglasses are reasonably effective blocks to radiative heat loss.

Infrared picture of a fellow wearing a black plastic bag on his arm. The bag is nearly transparent to heat radiation, while his eyeglasses are opaque. His hair provides some insulation.

As an illustrative example, lets calculate the radiative and conductive heat transfer heat transfer rates of the person in the picture, assuming he has  2 m2 of surface area, an emissivity of 1, and a body and clothes temperature of about 86°F; that is, his skin/clothes temperature is 30°C or 303K in absolute. If this person stands in a room at 71.6°F, 295K, the radiative heat loss is calculated from the equation above: 2 *1* 5.67×10−8 * (8.43×109 -7.57×109) = 97.5 W. This is 23.36 cal/second or 84.1 Cal/hr or 2020 Cal/day; this is nearly the expected basal calorie use of a person this size.

The conductive heat loss is typically much smaller. As discussed previously in my analysis of curtains, the rate is inversely proportional to the heat transfer distance and proportional to the temperature difference. For the fellow in the picture, assuming he’s standing in relatively stagnant air, the heat boundary layer thickness will be about 2 cm (0.02m). Multiplying the thermal conductivity of air, 0.024 W/mK, by the surface area and the temperature difference and dividing by the boundary layer thickness, we find a Wattage of heat loss of 2*.024*(30-22)/.02 = 19.2 W. This is 16.56 Cal/hr, or 397 Cal/day: about 20% of the radiative heat loss, suggesting that some 5/6 of a sedentary person’s heat transfer may be from black body radiation.

We can expect that black-body radiation dominates conduction when looking at heat-shedding losses from hot chemical equipment because this equipment is typically much warmer than a human body. We’ve found, with our hydrogen purifiers for example, that it is critically important to choose a thermal insulation that is opaque or reflective to black body radiation. We use an infra-red opaque ceramic wrapped with aluminum foil to provide more insulation to a hot pipe than many inches of ceramic could. Aluminum has a far lower emissivity than the nonreflective surfaces of ceramic, and gold has an even lower emissivity at most temperatures.

Many popular insulation materials are not black-body opaque, and most hot surfaces are not reflectively coated. Because of this, you can find that the heat loss rate goes up as you add too much insulation. After a point, the extra insulation increases the surface area for radiation while barely reducing the surface temperature; it starts to act like a heat fin. While the space-shuttle tiles are fairly mediocre in terms of conduction, they are excellent in terms of black-body radiation.

There are applications where you want to increase heat transfer without having to resort to direct contact with corrosive chemicals or heat-transfer fluids. Often black body radiation can be used. As an example, heat transfers quite well from a cartridge heater or band heater to a piece of equipment even if they do not fit particularly tightly, especially if the outer surfaces are coated with black oxide. Black body radiation works well with stainless steel and most liquids, but most gases are nearly transparent to black body radiation. For heat transfer to most gases, it’s usually necessary to make use of turbulence or better yet, chaos.