Reading List: The Diet Myth- Summary

TheDietMyth_orangeEvery scientist, researcher, and nutritionist has a potential to add to the understanding of how our bodies function and how the food we eat impacts health outcomes. We have published reviews from nationally-recognized  endocrinologists, gastroenterologists, nutritionists, neuroscientists, cardiologists, public heath authorities, and investigative-science journalists.

Dr. Tim Spector now contributes a new body of evidence to the mix. A physician and Professor of Genetic Epidemiology at King’s College London, he established the Twins UK register in 1993, and has been internationally honored for his pioneering genetic research. This Twins UK register is the largest of its kind in the world, and Dr.Spector continues to direct its research. Eleven-thousand sets of twins, identical and fraternal, participated in the register. He previously authored, Identically Different, a best-seller in the UK.

His latest poublication, The Diet Myth: Why the Secret to Health and Weight Loss is Already in Your Gut (February, 2016), relies on his extensive research in the field of genetics and provides an analysis of the role of digestive microbes that already exist in our stomach. It is a delightful and illuminating read.

Where else can you find data on the numerical impact genes have on the differences between people relative to body weight and fat (it’s about 70% genetic according to him), or on metabolism (genetic component is about 70% in sports, 50% for most other activities, and only 30 % while resting)? His book includes reviews of macronutrients (proteins, carbohydrates, fiber, fats), animal and non-animal proteins, vitamins, alcohol, cocoa and caffeine, and artificial sweeteners and preservatives, and compares the impact of foods on various populations.

The bulk of each chapter traces the historical evolution of various foods and their sourcing and then provides the current state of our knowledge on this list of topics. In concluding each chapter, he imparts his knowledge and what he believes is the genetic and microbial impact on the relative nutrition of these categories or foods or additives. Although it is thoroughly annotated and contains an excellent glossary, the majority of the text is easily understood and reads more like a fascinating food novel. Available on Audible Books, I listened each morning while walking the dog–a twelve hour investment, complete with exercise!


Saturated Fats: And Now the Cheese versus Butter Distinction

Over the 1980s-1990s, dietary-fat-leads-to-heart-disease was the prevailing nutritional hypothesis. Statin drugs became popular. In 2015, a study reexamined the finding of the early trials that showed an associated risk between the dietary fat and heart disease. Reducing cholesterol levels did not reduce heart disease.

A gold-standard randomized trial of high-dairy versus low-dairy has yet to be performed (earlier thought to be too risky or not practical to cover for years). In 2011, however, a twelve-week trial was performed on 49 volunteers. An initial low-fat diet was given all subjects for 6 weeks and then the subjects got 13 % more calories in the form of either cheese or butter. The cheese group didn’t increase blood lipid levels or cholesterol at all, but the butter group did. The conclusion drawn was that not all saturated fat is the same.( p. 53). Study reported in American Journal of Clinical Nutrition (2011); 94:1479-84.

Could Microbes be the New Fat Eater? The Yogurt Experiment

There is an increase in the general evidence of the benefits to eating probiotic-rich yogurts. And there has been “an emerging link between microbes and blood lipids.” (p.63). But there is little evidence that the friendly bacteria survive and replicate in the human gut, which means it must be eaten daily to derive benefit. (pp. 63-65). A carefully monitored seven-week study of identical twin pairs that provided yogurt with common microbes two times daily was found to have little or no impact on influencing other existing gut microbes. The experiment was repeated on mice with similar results.

On further examination, however, the scientists discovered that the yogurt microbes did have an impact on the activity level of the genes that “control the breakdown of complex carbohydrates and sugars found in fruit and vegetables.” (p.64). The conclusion reached was that introducing individual microbes might not alter the existing balance in our gut flora but it could have an impact on the metabolic balance of the microbes.

AUTHOR’S NOTE: Choose yogurts with a variety and high concentration of microbes or make your own. Many commercial brands overstate their benefits. And yogurts with sugars or puréed fruit could counter any benefits of eating probiotic-enriched products because the sugar stops the bacteria from growing. (pp.64-65).

Animal Protein: Metabolic Slow-Down and Impact of Microbes

Studies have demonstrated that after six weeks of intensive dieting or weight loss of 10%, the body compensates by slowing metabolism, and low-fat diets fare the worst in this regard. Dr. Spector points out that even high-protein diets “don’t fool the body for long” because cortisol levels ultimately rise and thyroid levels fall with the weight loss, having “the effect of increasing fat retention and reducing energy levels.” (pp. 110-111). The mechanisms are complex and, according to Spector, are “strongly influenced by genes as well as microbes.” (p. 111).

Tests on 49 subjects who were placed on a 1200 calorie diet (44% healthy high-fiber carbs, and 35 % protein) for six weeks then given an additional 240 calories (20%) for another six weeks, revealed that diversity of gut microbes was the biggest predictor of ultimate weight loss. Although everyone lost weight in the initial 6-week period, the quickest rebound occurred in the subjects with the least diverse microbial populations. An experiment with 292 Danish subjects produced similar results. “The low-diversity group was on average more obese and had higher insulin levels and visceral-fat plus abnormal lipids, giving them increased risk for diabetes and heart disease.” (p. 112).

The research also revealed that there were always keystone species of bacteria that were present in the healthy subjects with diverse populations: bifidobacteria F. prausnitzii, lactobacillus, and an ancient methane-gas producing bug. Dr. Spector compared it to the importance of keystone species in preserving biodiverse habitat like the wolves in Yellowstone.

Prebiotics and Microbe Fertilizers


According to Spector, recent studies have indicated that when levels of common prebiotic substances like inulin are measured, those numbers are similar to the amount of fiber we consume. Thus, a link has been established between  “the new science of prebiotics and the old fashioned concept of fiber.” (p. 183). Prebiotics are usually non-digested fibers that allow microbes to thrive, and act as microbe fertilizers. A healthy person may need about 6 grams of prebiotics a day to keep “their microbes and themselves healthy.” Good sources of key prebiotics are found in Jerusalem artichokes (sunchokes), dandelion greens, celery, leeks, onions, garlic, asparagus, wheat bran, and broccoli.

Mediterranean diets are likely beneficial not only because of olive oil, fish and nuts, but because the wide range and large quantity of foods with good fiber content. Onions, garlic, tomatoes, beans, chickpeas and cruciferous vegetables are regularly eaten. Fiber’s important benefits should not be overlooked and, it is the author’s opinion that we need to start consuming more of it. (p. 196).

Carbohydrate-Eating Gene Differences

Amylase is an enzyme produced in saliva and pancreas that breaks down starch in carbohydrates to glucose and energy. We all have different levels because of our genes. One pair of fraternal twins Dr. Spector studied experienced significant differences in weight their entire lives despite similar exercise patterns and eating habits including portion size. Tests revealed that the heavier twin had 5 fewer copies of the amylase gene than did her thinner sister. According to Spector, the risk of obesity increases by 19% for each copy of the gene in which you are deficient. In the subject twin pair he studied, the risk was about double between one sister and the other.

A Potato is Not the Same for All of Us

Until recently, it was believed that the majority of the genes impacting obesity acted on the brain. In other words, they caused signals to the brain that led to overeating or a lack of willpower when presented with certain foods. What has recently been discovered, however, is that the metabolic effects of these genes are actually ten times greater than the influences on the brain. (p.194)

Dr. Spector analyzed the metabolic patterns of the twins with the highest levels of difference in copies of the amylase genes. He found that there were major distinctions in the microbial communities that may have been triggered by the altered digestion of starches in the twin with the fewer amylase gene copies. It also seemed to result in the production of different fatty acids. The result being that:


Chewing or Sipping Your Carbs?

Our bodies have been designed to chew and swallow food slowly, even though we use our jaws less than our ancestors–up  to forty chews (but I can’t think of anyone with the time or patience for that!). Well-chewed and broken-down food moves through our system, releasing hormones from our gut lining, liver, pancreas and gall bladder to aid in the digestion. Insulin is released from the pancreas so that glucose in the bloodstream can be dealt with. The gall bladder releases salts which send signals to the microbes further down the gut to get ready to digest food.

But if you drink a sugary drink and consume quickly-chewed pasta, havoc ensues. The food rapidly reaches the small intestine where most of the sugar is absorbed which then causes a mistiming in the release of insulin. And the bile salts have released a different and unhealthy kind of microbe to deal with the sugar scraps. The normal gut microbes then send out signals asking for more sugar because they haven’t received any food from the sugary meal that was mostly absorbed in the small intestine. Result: the glucose then gets stored away as fat, “often of the internal (visceral) kind.” (p.161).

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