ESSENTIALS: NUTRITION

Several studies support the hypothesis that diet, particularly carbohydrate consumption, affects vision. One study compares the eyesight of hunter-gatherer and industrialized groups and finds myopia skyrockets when indigenous populations adopt a Western diet involving more refined carbohydrates. Another study explores the mechanism behind dietary contribution to myopia and finds increases in insulin promote eyeball elongation in animal models. A third study explores dietary sugar’s links to glaucoma, cataracts, diabetic retinopathy, and macular degeneration. Its authors ultimately recommend avoiding high glycemic index foods.

Georgia Ede argues the dramatic fluctuations in glucose and insulin levels caused by eating high-glycemic-index foods lead to a variety of negative psychological effects.

A 2016 review finds preliminary evidence suggesting intermittent fasting and similar eating patterns can reduce markers of cancer risk and progression. More intensive fasts, such as complete fasting on alternating days, show more consistent benefits; more moderate fasts show equivocal clinical impact.

This brief 2017 review surveys evidence that suggests increased consumption of added sugars increases heart disease risk, both indirectly by increasing the risk of diabetes and directly through other mechanisms.

Three case reports demonstrate durable (in two cases permanent) remission of Type 1 diabetes through the introduction of a low-carbohydrate diet soon after diagnosis.

Previous research has suggested intermittent fasting drives metabolic benefits independent of weight loss, including improvements in insulin sensitivity, lipid profile, liver fat, and markers of inflammation and oxidative stress. This 2018 trial assessed the metabolic benefits of a specific form of intermittent fasting: early time-restricted feeding, where all food intake was confined to a single six-hour window early in the day. Researchers found subjects who ate within that window improved insulin sensitivity and beta cell functionality as well as blood pressure and markers of oxidative stress.

“The reaction [to the Annals of Internal Medicine publications debunking the advice to eat less meat] was swift and unsurprising. Proponents of the current guidelines were quick to attack the papers and the authors. The first thing that I noticed in the first media article I read was that the word “controversial” appeared in the first sentence. … A (essentially, if not entirely) non-conflicted panel published four systematic reviews of all the evidence available (which was vast for observational studies, if not RCTs) and concluded that any associations observed were very small and the certainty of evidence was low or very low. They cautioned that observational studies cannot establish causation; they don’t report absolute differences; and they are at high risk of confounding. My conclusion from this would have been to dismiss existing guidelines and advise that they be ignored. The panel’s recommendations to continue current consumption were cautious in this context, not controversial.”

This 2018 review describes the causes and benefits of “flipping the metabolic switch” — that is, using fasting to transition the body from a state of fat storage to one of fatty acid release and oxidation.

“Blood-vessel disease was common (among the ancient Egyptians), contrary to assumptions that it arises from urban stress and a modern high-fat diet,” Dr. Michael Eades, MD, reads aloud to the audience at the CrossFit Health Conference on Aug. 1, 2018. After reading this quote in a book, Eades began to research the dietary factors that may have contributed to the high incidence of heart disease among the ancient Egyptians. In this presentation, Eades shares some of the outcomes of that research, taking his audience “on a journey through the anthropological literature and what that means in terms of ‘off the carbs.’”

This 2017 review summarizes the potential of a ketogenic diet to enhance the effects of radiotherapy. Radiotherapy is constrained by the damage it causes to healthy cells. As a result, any simultaneous treatment that can either increase the damage radiotherapy does to cancer cells or protect healthy cells from damage may increase its effectiveness. Potential benefits of a ketogenic diet alongside radiotherapy include the reduction of cancer cells’ ability to repair DNA, the slowing of tumor growth and repopulation, and the protection of healthy cells against the harms of radiotherapy by shifting them from an anabolic/growth-centric state to a non-dividing state.

This 2019 case study demonstrates a reversal of long-term diabetes and depression through carbohydrate restriction and exercise.

This brief 2019 article reviews the timeline and consequences of the dramatic increase in sugar consumption in the U.S. and Western world.

“What scientists do and what journalists do are similar in that we’re both supposed to be establishing reliable knowledge about the universe,” Gary Taubes told the audience at the annual CrossFit Health Conference on July 31, 2019. Taubes, an award-winning investigative journalist, has spent the last several decades turning a critical eye toward places where received wisdom in the fields of science and medicine has diverged from reliable knowledge. In this presentation, he evaluates what the experts say about why we get fat and explains why has become a critic of the consensus.

Over the past 40 years, sugar intake (and thus fructose intake) has increased dramatically in Western diets, rising to 15-17% of total daily caloric consumption. This rise comes alongside increasing evidence linking fructose to diabetes, fatty liver disease, and cardiometabolic risk factors. This brief 2019 review summarizes the mechanisms by which fructose drives these metabolic diseases.

Type 2 diabetes is generally thought to be chronic and progressive, marked by an inevitable decline in beta cell function and increase in plasma glucose levels. Current pharmaceutical treatments are fundamentally unable to alter the course of the disease. Bariatric surgery has been shown to rapidly normalize glucose levels, even prior to weight loss. This study tested whether severe caloric restriction — similar to that seen alongside bariatric surgery — could lead to similar glycemic benefits. The study found that a very low-calorie diet rapidly improves liver insulin sensitivity and gradually improves pancreatic function in the process reversing Type 2 diabetes.

In the 1950s, Ancel Keys worked to make the diet-heart and lipid hypotheses famous, leading to the decades-long demonization of saturated fat and cholesterol that has continued to shape the Western diet ever since. Here, Prof. Tim Noakes levels several critiques at Keys’ influential research. Noakes compares Keys’ claims to the data and sources upon which they are based and determines Keys’ evidence is weak, associational, and epidemiological at best, and wilfully deceptive at worst. While the inadequacy of Keys’ evidence has been discussed before, Noakes adds to the conversation by arguing Keys’ major findings are derivative of earlier research by Drs. Haqvin Malmros and John Gofman — research Keys strategically sought to discredit, according to Noakes. Noakes also discusses the historical context in which Keys developed his theories in order to shed light on some possible motivations for Keys’ subterfuge.

Oxygen, the very thing that gives us life, can also be life-threatening, under certain circumstances increasing the risk for central nervous system oxygen toxicity (CNS-OT) seizure. CNS-OT seizures are a limitation of both hyperbaric oxygen therapy and scuba diving, particularly among Navy SEALS who use closed-circuit rebreathers. Dr. Dominic D’Agostino, an expert in the neuroprotective effects of the ketogenic diet, explains why ketones were investigated as a possible mitigator of CNS-OT seizures. He also summarizes existing research on the effects of exogenous ketone supplements on CNS-OT, describes the potential mechanisms at work, and lists examples of ketones' protective qualities.

In September 1955, President Dwight D. Eisenhower experienced an acute anterolateral myocardial infarction. Dr. Paul Dudley White of Boston’s Massachusetts General Hospital joined the attending military doctors in treating the president. Eisenhower lived another 14 years but suffered from a slew of chronic diseases during that time, diseases Prof. Tim Noakes attributes to White’s prescription of an untested, experimental diet. Like the diets associated with Ancel Keys’ incorrect diet-heart and lipid hypotheses, which laid the foundation for dietary guidelines promoted for decades by the American Heart Association and American Diabetes Association, White recommended the president follow a low-fat, low-cholesterol, high-carbohydrate diet. Eisenhower, a model patient, followed the recommendation, but his health markers began to trend in the wrong direction. Noakes theorizes about why the treatment ultimately failed, and why we have continued to fail to learn from the mistake.

This 2016 paper describes four common variations of the ketogenic diet and reviews the effects of the ketogenic diet on cancer, neurodegenerative disease, and specific inherited conditions. Though research on the diet’s effects on these specific conditions remains preliminary (i.e., in vitro or animal), existing data suggest ketogenic diets may have clinically significant benefits.

Previously in this series, Prof. Tim Noakes argued Dr. Gerald Reaven was on the brink of discovering the optimum treatment for insulin resistance syndrome, a condition he called “Syndrome X.” In this post, Noakes delves further into the scientific literature available to Reaven as he formulated dietary recommendations for patients with the condition. The prevailing theory at the time suggested carbs were an essential part of a healthy diet and cautioned that the consumption of saturated fats would promote heart disease. Tragically, despite the contrary indications of his own research and a growing body of evidence revealing the detrimental effects of carbohydrate ingestion in persons with insulin resistance or Type 2 diabetes, Reaven ultimately bowed to the influence of Keys and other diet-heart hypothesizers and promoted a diet closer to that recommended by the American Heart Association — a diet Noakes argues has caused the rates of obesity and Type 2 diabetes to soar around the world.