Ask anyone in the medical community over the last thirty years, what kind of diet they recommend as optimum for weight control, general health, and athletic performance, and the nearly universal answer would be one low in fat and high in carbohydrates.
Yet, following that advice, writes Dr. Peter Brukner in the British Journal of Sports Medicine, has only resulted in a steady increase in western countries of the incidence of obesity and type 2 diabetes.
Now scientists are starting to challenge conventional wisdom. At the forefront of those questioning this core principle of sports nutrition, says Brukner, is Professor Tim Noakes from the University of Cape Town, the same scientist who, in his controversial book, "Waterlogged," raises questions about another core principle of sports nutrition: that thirst is not a good indicator of hydration status , and the belief - accepted as gospel, truth be told, in articles on this website for the past 13 years - that athletes should drink lots of fluids before, during, and after exercise . (In fact, Professor Noakes' argument, that drinking too much water can lead to fluid retention and exercise-associated hyponatremic encephalopathy (EAHE) or 'water intoxication,' is the subject of two recent articles by MomsTEAM experts, one by sports nutritionist Nancy Clark , and the other by sports hydration expert, Dr. Susan Yeargin )
Having himself converted from a high carbohydrate to low carbohydrate high fat diet with impressive results, Noakes now advocates its use by those with impaired carbohydrate metabolism associated with type 2 diabetes, or its precursor 'metabolic syndrome'. Specifically, Noakes recommends eliminating bread, grain, pasta, rice and potatoes, along with sugar-laden soft drinks and fruit juices, from the diet, while at the same time increasing intake of saturated fats, which contain important nutrients but, according to studies, don't increase levels of so-called 'bad' cholesterol and triglycerides.
Why cut back on carbs and increase fat intake? Noakes and other advocates of the low carbohydrate diet, writes Brukner, point to insulin as the culprit. The theory they advance is that, because insulin is secreted by the pancreas in response to carbohydrate ingestion - not in response to fat or protein - the more carbohydrate ingested, the more insulin is secreted. After the initial increase in blood glucose after a carbohydrate intake, the subsequent blood glucose drop causes hunger, they say. The high level of insulin in those ingesting large amounts of carbohydrates is thought to lead to insulin resistence, where more and more insulin is required to lower the blood glucose concentration. Insulin may also be responsible for the conversion of excess carbs into triglycerides in the liver, which are then released into the bloodstream.
"The low carbohydrate advocates," Brukner continues, "claim that their diet reduces the levels of insulin and therefore the conversion of carbohydrate into body fat" and also to other possible advantages of maintaining low blood insulin (and glucose) concentration, "since persistently high insulin concentrations may be linked to accelerated ageing, mental decline, and perhaps even specific cancers."
Where does that leave athletes, who, Brukner correctly notes, have "long been encouraged to load up with carbohydrates prior to and during endurance exercise  because glycogen, the ... form of carbohydrate [stored by the body], was thought to be a more efficient fuel than fat"?
Well, that recommendation has come under recent attack as well, says Brukner, by scientists arguing that fat provides more calories per gram and also has much larger body stores. Noakes, for one, argues that "after a week or two of carbohydrate deprivation, our bodies change from a carbohydrate metabolism to a fat metabolism with health and performance improvements."
While it would seem that fat is just as effective a fuel for endurance events, however, says Brukner, what remains unclear is whether a high fat low carbohydrate diet is appropriate for athletes in intermittent high-intensity sports such as [soccer] or road cycling.
Have the nutrition experts raising questions about the effectiveness of low fat diets made any headway? Not so far, Brukner says, as the "vast majority of profession and all advisory bodies still defend, in some instances quite vehemently, its use, especially in the prevention of cardiovascular disease," with some expressing concerns about the safety of low carbohydrate diets over the long term.
Not surprisingly, the debate, he notes, is complicated by individuals, organizations, and industries, such as the food, agricultural and pharmaceutical, which have a vested interest in maintaining the status quo.
"What is urgently needed," Brukner concludes, "is a totally objective scientific review of the existing evidence, and support to obtain any further evidence required to answer what he says "surely is the most important single question in medicine at the moment. ... We need to determine once and for all whether our profession's universal recommendation of a low fat high carbohydrate diet is the correct one.
According to Amy McKenzie, a doctoral candidate at the University of Connecticut, many of the ideas Dr. Noakes has been implementing in his lifestyle are the result of research published by Jeff S. Volek, PhD, RD and Stephen D. Phinney, MD, PhD, among many other contributors. Volek and Phinney recently published two books about low carbohydrate living  and performance  which contain much more information about the science behind this diet.
"Insulin level is one idea that definitely has scientific support within low carb/high fat diets," says McKenzie. "Since insulin is an anabolic (or building) hormone, it allows for glucose (the building block for carbohydrates) to be brought into the cell and for the glucose that isn't immediately used to be stored as fat when blood insulin and glucose levels are high. However, if blood glucose level is kept to a minimum, a large insulin release doesn't occur and this storage of fat is prevented. So for those using the diet for weight loss (and thus reduction of cardiometabolic risk and overall health), this is a large contributing factor."
McKenzie continues that, "Beyond just reducing storage of excess glucose as fat, maintaining low insulin levels also impacts many different health outcomes. A few studies have shown associations between high insulin levels or insulin resistance and some cancers (breast, colon, and prostate to name a few). And when considering low carb/high fat diets as a whole, studies have demonstrated them to be useful in treatment for metabolic syndrome, diabetes, seizure disorders, autism, and reducing blood pressure and other markers of cardiovascular disease."
"Regarding athletic performance, we know a little bit, but definitely not everything. Many of the studies that report negative effects of a low carbohydrate diet did not use an appropriate distribution of carbs, fats and proteins to be considered the low carb/high fat diet we're talking about here, or the study did not allow the subjects enough time on the diet to fully adapt to their new means of metabolism where fat is more efficiently utilized as a fuel source," says McKenzie, who is careful to note that, "we don't know exactly how long it takes to adapt either and this might vary between people."
"Another thing to consider is the amount of salt and potassium lost in urine while on low carbohydrate diets. If these electrolytes aren't adequately replaced, athletic performance might also be negatively impacted. So although the scientific literature is a little muddy about exactly how a good low carb/high fat diet impacts athletic performance, I'd venture a guess, based on anecdotal evidence and logic, that after considering all of those things (time to adapt, proper nutrient proportions, and adequate salt/potassium intake), a low carb/high fat diet doesn't necessarily have a negative impact on performance, especially for endurance to ultra-endurance athletes," McKenzie concludes.
Strength and conditioning trainer Mike Boyle echoes this advice in talking nutrition with 4-time Olympic medalist Angela Ruggiero: "This high carb, low fat thing has only given us a higher incidence of diabetes and hasn't done much else for the country. We're fatter and sicker, so I have to believe it's not working real well."
Boyle advises the athletes he trains to eat more high quality protein, and to eat more vegetables.
1. Brukner P. Challenging beliefs in sports nutrition: are two 'core principles' proving to be myths ripe for busting? Br J Sports Med. 2013;47:663-664.
2. Noakes TD. Waterlogged: The Serious Problem of Overhydration in Endurance Sports. (Champaign, IL; Human Kinetics, 2012).
3. Noakes T. Tim Noakes on carbohydrates. http://www.health24.com/Diet-and-nutrition/Nutrition-basics/Tim-Noakes-o... .
Most recently updated November 12, 2013 to include the Mike Boyle/Angela Ruggiero video clip.