Wednesday, August 1, 2012

It's The Diet, Stupid!

Apparently it’s our diets, not our lack of exercise, that is responsible for rising rates of obesity and the explosion of metabolic diseases:
A study of the Hadza tribe, who still exist as hunter gatherers, suggests the amount of calories we need is a fixed human characteristic. This suggests Westerners are growing obese through over-eating rather than having inactive lifestyles, say scientists.

One in 10 people will be obese by 2015. And, nearly one in three of the worldwide population is expected to be overweight, according to figures from the World Health Organization. The Western lifestyle is thought to be largely to blame for the obesity "epidemic".

A team of scientists from the US, Tanzania and the UK, measured energy expenditure in 30 Hadza men and women aged between 18 and 75. They found physical activity levels were much higher in the Hadza men and women, but when corrected for size and weight, their metabolic rate was no different to that of Westerners.

Dr Herman Pontzer of the department of anthropology at Hunter College, New York, said everyone had assumed that hunter gatherers would burn hundreds more calories a day than adults in the US and Europe. The data came as a surprise, he said, highlighting the complexity of energy expenditure. But he stressed that physical exercise is nonetheless important for maintaining good health.

"This to me says that the big reason that Westerners are getting fat is because we eat too much - it's not because we exercise too little," said Dr Pontzer.
Hunter gatherer clue to obesity (BBC)

What this also debunks is the notion that hunter-gathers had to work super-hard and burn all these calories to put food on their metaphorical plate. Plus they weren't sitting in a chair for eight hours a day. Here's the New York Times on the study: Dieting Versus Exercise for Weight Loss. And as for the content of those diets:
Members of Southwest Native American tribes are more susceptible than Caucasians to Type II diabetes, which happens when the body either doesn't produce enough insulin to break down sugar from food, or when the body's cells fail to recognize the insulin it does produce. Researchers have long hypothesized that a "thrifty gene" (or, more likely, genes) acquired through feast and famine makes Native American populations more prone to this chronic disease. The idea is that people who were able to rapidly adapt to both lean times and times of plenty would have done better in ancient times. Today, the modern diet has rendered famine rare in the developed world, but the body continues to respond to times of plenty as if starvation is around the corner. Diabetes and obesity can result.

Reinhard and his colleagues now suggest that feast and famine may not be necessary for the "thrifty gene" hypothesis to make sense. Basically, Reinhard said, an extremely low-calorie, high-fiber diet made the ancient Native American gut a paragon of efficiency. With the arrival of whites, the diet changed faster than physiology could keep up with it. In other words, the digestive system didn't evolve for abundant, high-GI foods.

The analysis revealed that these ancient people chowed down on flour made from maize and wild sunflower and other seeds, as well as on fibrous succulent plants such as yucca and prickly pear. This diet was higher fiber than anything modern people eat. The feces were three-quarters fiber by volume, Reinhard said, and these Native Americans were probably eating between 200 and 400 grams of the indigestible stuff per day. For comparison, the Institute of Medicine recommends 25 grams of fiber a day for the modern woman, and 38 grams for men. The average adult manages only about 15 grams. [8 Reasons Our Waistlines Are Expanding]

Modern agriculture has favored plants with less fiber, Reinhard said, so even the ancient tribes' maize would have been more fibrous than the corn we eat today. "When I was a young researcher I tried to replicate this diet, and it was impossible," Reinhard said. "I was essentially eating all day to try to get this fiber."

In addition, Reinhard and his colleagues reported in the August issue of the journal Current Anthropology, the Southwest Native American diet had a very low glycemic index. Prickly pear pads, a common staple, rate only a 7 on the 100-point GI scale. The highest-GI food these tribes would have had was maize, the researchers found, which would fall at about 57 on the scale — just two points shy of qualifying as a "low-GI" food today. (Modern sweet corn on the cob has a GI of 60; processed foods like white rice and bagels are in the 90-95 range.)

In addition, prickly pear has a known blood-sugar-lowering effect, Reinhard said. Agave and yucca plants would have also had minimal effect on the blood sugar while providing yet more fiber. Rabbit, including bone fragments, was also found in the fecal fossils.

"The change we have undergone over generations has been toward less appreciation of really resistant foods and more toward what is called a 'Pablum' diet," Reinhard said. "It's kind of like going from chewing on pumpkin seeds to chewing on oatmeal." The diet seen in the desert Southwest up to just 1,000 years ago is likely similar to what people ate the whole world over up until about 15,000 years ago, Reinhard said. And then humans invented agriculture, cultivating wheat, millet, rice and other grains.

"These plants, as they were cultivated, replaced the really, really ancient foods that everybody ate thousands and thousands of years ago with calorie-dense foods, or grains that could be turned into calorie-dense foods like grains, rice cakes, and, of course, alcoholic beverages," Reinhard said.
Ancient Poop Gives Clues to Modern Diabetes Epidemic (LiveScience)

Unfortunately, our simulacrum of food is going to be affecting us for a long time: Your Diet Affects Your Grandchildren's DNA, Scientists Say (LiveScience)
You are what you eat, the saying goes. And, according to two new genetic studies, you are what your mother, father, grandparents and great-grandparents ate, too.

Diet, be it poor or healthy, can so alter the nature of one's DNA that those changes can be passed on to the progeny. While this much has been speculated for years, researchers in two independent studies have found ways in which this likely is happening. The findings, which involve epigenetics, may help explain the increased genetic risk that children face compared to their parents for diseases such as obesity and diabetes.

The punch line is that your poor dietary habits may be dooming your progeny, despite how healthy they will try to eat. Epigenetics refers to changes in gene expression from outside forces. Different from a mutation, epigenetic changes lie not in the DNA itself but rather in its surroundings — the enzymes and other chemicals that orchestrate how a DNA molecule unwinds its various sections to make proteins or even new cells. 
Recent studies have shown how nutrition dramatically alters the health and appearance of otherwise identical mice. A group led by Randy Jirtle of Duke University demonstrated how mouse clones implanted as embryos in separate mothers will have radical differences in fur color, weight, and risk for chronic diseases depending on what that mother was fed during pregnancy. That is, the nutrients or lack of thereof changed the DNA environment in such a way that the identical DNA in these mouse clones expressed itself in very different ways.
As this comment to the Times article says: “Someday we should take a hard look at what passes for food. HFCS, many artificial sweeteners, GM food, Foods fried in GM modified canola oil. The list goes on and on.  And while we are looking don't forget that obesity is not our only problem. It is accompanied by an epidemic of autism and an increase in Alzheimer's disease. It may be that the cheep foods we eat are costing us a terrible price.” Indeed, another casualty of "modern" lifestyles. Indeed, emotional states can also alter fetus' genetic expression, meaning that a socially disordered and unequal society will literally change its people at the genetic level.

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