Anyone keeping a healthy lifestyle knows that temptation is all around. Convenience stores and fast food outlets alternate on every corner. Marketers pay food psychologists to design sales tactics that overcome our will power and best intentions. Intentional combinations of fat, sugar and carbohydrates, engineered by food scientists, get us hooked on junk food in much the same way we are hooked on drugs.
We are aware of that environment. But there are other environments we cannot see that are attracting the scrutiny of researchers – the colony of bacteria in our intestines, activity within our brains and the weird ability of our intestines to expand and contract.
There is no doubt that night shift work is associated with weight gain and obesity. No one knows exactly what goes on inside our brains to make us fat when we work at night, but we know it happens.
A 2018 meta-study reveals interesting and puzzling details.
Combing the results of 28 studies of weight gain and shift work found that working at night increased the risk of being overweight by 23%, however the increased risk of dangerous abdominal or belly fat was even greater at 35%.
Robert Lusting, in his revolutionary book, Fat Chance, tells us all bout abdominal fat and why it is so dangerous.
Fat comes in a different varieties, and not all of them are bad.
Subcutaneous fat is “healthy fat” laying just under the skin. It is what gives women their curves, provides energy reserves when we are sick and seems to protect against disease. Elderly people without a modest amount of subcutaneous fat get sick more often, die younger and experience more injuries than those with a healthy amount.
Visceral fat – that kind that collects around our middle – it’s what kills us. Visceral fat causes insulin resistance, and insulin is the main player in how we digest our food. According to Lusting, insulin resistance promotes diabetes, cancer, cardiovascular disease, dementia and general ageing.
Our body easily turns visceral fat into energy to fuel our muscles and organs. But that leads to one of the very dangerous aspects of visceral fat – it resides near our organs. We can’t see the damage visceral fat does when it surrounds our liver or heart, but that is the essence of metabolic disease.
The only place we can easily detect visceral fat is when we see it around our belly. Lusting cites studies indicating that our waist circumference is the best predictor of risk of death from metabolic diseases. In other words, belly fat is a proxy or symbol for dangerous intra organ fat. But how do we measure it? How can we tell how much risk our visceral fat is subjecting us?
Lusting offers three suggestions.
First is belt size. Anything more than 40 inches for men or 35 inches for women is a likely indicator of excess visceral fat.
Another easy way to spot excess visceral fat is looking for darkening, thickening or ridging of the skin around the neck, armpits or knuckles. Lusting says this is excess insulin reacting with hormone receptors just under the skin.
For a more accurate measure, calculate the ratio between waist and hip. Research suggests that ratio less than .80 indicates a healthy amount of visceral fat. (Interestingly, David Buss, a well-known researcher and author of The Evolution of Desire finds that men consistently prefer women with a waist-hip ratio of .70.)
But why would shift work have anything to do with gaining visceral fat?
Barbara Natterson-Horowitz, MD, explains the biology behind circadian rhythms in her book Zoobiquity.
All the cells in our bodies contain “oscillators” built by clock genes. These oscillators influence the timing of everything in our bodies – how fast calories burn to when we feel like eating. Plants, animals, bacteria and even single celled organisms manage circadian rhythms.
Creatures with complex brains have a collection of neurons coordinating all these oscillators. Located at the point where the optic nerve connects to the hypothalamus is a tiny brain structure about the size of a sesame seed. Called the suprachiasmatic nucleus, (SCN), this tiny organ detects light levels detected by the optic nerve and directs our circadian rhythms – that is, helping us to sleep at night and remain awake during the day.
Think of its job as synchronizing external time signals with our internal oscillators.
When researchers expose mice to constant light, even dim light, they gain weight and carry higher blood-glucose ratios than mice exposed to natural rhythms of light and darkness. We also know that plants and animals living further from the equator have lower levels of sugars in their systems.
The annual switch from standard time to daylight savings time creates an opportunity for research on disruptions to circadian rhythms. Researchers find that depression increases during the switch to daylight savings time, as do car accidents, heart attacks and stoke. And that is just a modest change of one hour.
We know that lack of sleep can contribute to weight gain. In his book Go Wild, John Ratey, MD, points out that sleep deprivation studies consistently show that lack of sleep is associated with weight gain, even though there is no measurable change in caloric intake or energy expenditure.
It is interesting to point out that researchers have a hard time controlling for increased caloric intake when doing sleep deprivation studies. Simply not getting enough sleep causes disruption of hormones that signal satiety, resulting in cravings for sugar and carbohydrates, especially in the evening.
Putting all this together shows us that there is a complicated interplay between light, sleep and the secretion of hormones that affect our appetite, even to the point of causing a desire for certain foods.
But there are even more things that we have very little awareness of, yet can have far-reaching effect on how we gain, lose and carry our weight.
Natterson-Horowitz spends quite a bit of time telling us about our intestines and what scientists are finding in them.
The intestines of many animals can contract or expand. The remarkable ability to change the length of intestines is common among animals that migrate and hibernate. Fish, frogs, snakes squirrels voles and mice all have this ability. The exact mechanism is unknown, but it probably related to circadian rhythms. When stretched out intestines can absorb more nutrients from food passing though. They become more efficient.
It is unsettling to think that is one more thing we can’t control that affects our weight.
However, we are learning far more about our biome – the collection of microbes who call our intestines home. At birth, we have no intestinal microbes – our innards are sterile. This changes as we are exposed to microbes in our environment.
Parents can tell when their babies develop gut microbes – diaper changing suddenly becomes a very smelly affair. By the time we are only a few months old trillions of microbes reside in our mouths, skin, teeth, even our lungs. It is thought that only about ten percent of the cells in our body are human. The rest are little friends we pick up from the environment.
There are two dominant types of bacteria in our biome, firmicutes and bacteroidetes. Firmicutes are associated with obesity and bacteroidetes with leanness. Obese individuals tend to have more firmicutes bacteria in their gut biome than people with a normal weight do.
Each of us has a unique blend of these microbes, which accounts for the differences in how what we eat affects our weight. Some people can eat pasta and wine without giving their weight a thought, while others have to be careful about eating an apple or avocado.
It turns out that bacteroidetes are far more efficient at extracting calories from food than firmicutes are. When obese people lose weight, the ratio of firmicutes to bacteroidetes changes, and bacteroidetes eventually out number firmicutes.
Whether or not we can change the ratio of firmicutes and bacteroidetes and lose weight by taking probiotics is an open question. But not for the weight loss industry. They are taking advantage of the discovery and offer us a range of products designed to increase gut bacteroidetes. How much of an effect these products have on weight is hard to determine.
At this point, you might be wondering whether the controversial practice of giving farm animals high doses of antibiotics has an effect on the humans who eat them. Agribusiness is no longer allowed to administer massive doses of antibiotics for purely preventive measures.
However, the rules are very liberal, and routine use of antibiotics allows animals to get fatter on less food. Exactly why this happens is unknown, but it is possible that some gut microbes like firmicutes are more resistant to antibiotics than others are. The effect that antibiotics administered to farm animals has on the humans who eat them is unknown.
Scientists are making discoveries almost daily showing how intimately interconnected we are with our environment. The more we learn, the better we can make decisions pointing us to a long and healthy life.
Books mentioned in this article:
Buss, D. M. (2003). The evolution of desire: Strategies of human mating (Revised ed.). New York: Basic Books.
Lustig, R. H. (2012). Fat chance: Beating the odds against sugar, processed food, obesity, and disease. New York, New York: Hudson Street Press.
Natterson-Horowitz, B., & Bowers, K. Zoobiquity: What animals can teach us about health and the science of healing (1st ed.). New York: Alfred A. Knopf.
Ratey, J. J., Manning, R., & Perlmutter, D. (2014). Go wild: Free your body and mind from the afflictions of civilization (First edition. ed.). New York, NY: Little, Brown and Company.
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