ACSM 2016 – “Nutrition and Athletic Performance,” by the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine (2016)

Quite the document and worth reading. I don’t mean to suggest that consensus documents from big public health institutions are generally very useful for athletes, especially teenage athletes. They aren’t. This one is, though. It is focused on athletes. And it calmly deals with a number of superstitions often heard on the pool deck.

Highlights:

  • Crashing blood sugar: Conventional advice holds that athletes should seek out snacks with higher fiber and ‘natural’ sugars (derived from fruit). The rationale is that these nutrients will help prevent spikes and crashes in blood sugar. But among the most strongly supported findings presented on carbohydrates and training is the simple observation that these supposed blood sugar spikes and crashes do not affect athletic performance.
  • Sucrose. The best source of quick energy (based on the evidence reviewed here) is glucose + fructose. And common table sugar is glucose (50%) + fructose (50%). So don’t overthink it. (2) 
  • Protein: Consume some protein during recovery.
  • Beware ‘low-energy availability!’ The report rings the alarm bells. Teenage athletes can be eating normally, participating fully in their sport, performing academically, and acting like a normal teenager while running up a potentially dangerous deficit in energy intake. First to suffer are unseen metabolic processes like bone density maintenance. Don’t let this happen.
  • Dietary fat: ‘Fat is a necessary component of a healthy diet, providing energy, essential elements of cell membranes and facilitation of the absorption of fat-soluble vitamins.’
  • Saturated fat: The report notes (at arm’s length) that two government agencies recommend restricting saturated fat to 10% of total caloric intake. Those agencies cite, as the basis for that restriction, studies on dietary fat and heart disease. Those studies are controversial. (1) The ‘10%’ number is a mystery. It does not come from the studies. The highly influential Institutes of Medicine nutritional guidelines estimate that in most diets, saturated fat will be about 10% of total calories. But that’s an estimate, not a limit, and the IOM is very clear that 10% is not a restriction.
  • Very-low carbohydrate diets are probably not a great choice for swimmers.
(1) In just about every case, reducing saturated fat intake made no difference for otherwise healthy people. The one exception was odd. Older people with bad lipid panels appeared to get some small benefit by substituting polyunsaturated fat for saturated fat. And the benefit was dubious. They were (slightly) less likely to be diagnosed with heart disease. But no less likely to DIE from heart disease. Put another way, if your concern is whether you DIE from heart disease, then these studies provide no evidence that you should reduce your consumption of dietary saturated fat.
(2) Though not covered in this report, fructose (fruit sugar) metabolism is pretty cool. Unlike glucose, most cells in the human body cannot use fructose directly. So the body sends the fructose to the liver (mostly) where it is converted into mostly glucose, along with some lactate, and a little fat (triglyceride). All three components can be used by skeletal muscle for energy production. Fructose conversion is its own weird little pathway. And that’s a good thing. Because during exercise, when glucose utilization is maximally stimulated, you can increase overall muscle energy provision by adding fructose to the mix. Sounds great. But where can we find glucose and fructose conveniently packaged together? Basically, everywhere. Brown sugar, white sugar, cane sugar, beet sugar, high-fructose corn-syrup, barley malt, molasses, honey, agave syrup, etc are combinations of glucose and fructose.

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