Stephen D. Phinney

During endurance sports, maintaining high carbohydrate availability is challenging, whereas switching to lipid fuels with the selective partitioning of ketones among organs could be revolutionary for athletes.

The argument that you need a high carbohydrate intake and high insulin levels to replenish glycogen reserves is a moot point if you are keto-adapted, since your use of glycogen during exercise will be dramatically reduced. This would be like worrying about putting regular gasoline in your tank when your vehicle has a diesel engine.

The direct metabolic benefits of keto-adaptation translate into two general effects relevant to most athletes. 1. Improved body composition (power-to-weight ratio) 2. Improved prolonged endurance performance resulting from better sustained fuel delivery.

The primary nutrient that stimulates insulin is dietary carbohydrate. Some forms of carbohydrate stimulate insulin more than others. Thus, consumption of insulin-stimulating carbohydrates is a surefire way to inhibit your access to the energy stored as body fat during and after exercise.

One implication of this adaptation is protection from ‘hitting the wall,’ an event primarily associated with inadequate fuel for the brain. This problem (aka ‘bonking’) occurs in the non-keto-adapted athlete when muscle and liver glycogen reserves are exhausted, leaving muscle and brain to compete for the relatively small amount of glucose that can be made by gluconeogenesis from protein. In addition to improving fuel availability during prolonged exercise, the keto-adapted state may also protect against central fatigue.

Most of the fat in prepared mayonnaise, dressings, sauces, and marinades is the wrong kind for a person on a high fat diet—high in polyunsaturated fat (PUFA) from the cheap, government subsidized soy, corn, and cottonseed oils used as ingredients.

We live in interesting times. May we continue to work together until that day when, walking down the street, we find that obesity is once again rare and no longer the norm.

Simply put, there is no option for weight maintenance that is simultaneously low in carbohydrate and low fat. Your energy has to come from somewhere, and for people with carbohydrate intolerance, their best (and safest) long-term energy source is dietary fat. ... Our point here is that with your dietary carb intake constrained by your individual level of carbohydrate tolerance (be it 40 or 100 grams), you must get comfortable eating fat as your primary source of dietary energy if you want to succeed in low carb maintenance.

Put simply, consuming too much carbohydrate is like metabolic kryptonite if you already have insulin resistance.

So what is the verdict in the ‘whodunit’ case? The culprit is our excessive intake of insulin-stimulatory dietary carbohydrates, especially simple sugars and refined starches. Lock enough of them up permanently, and the metabolic crime spree will end. Good work detective—metabolic syndrome solved—case closed!

Even if you thrive on a low fat diet now, carbohydrate intolerance is increasingly prevalent as we age. Thus, over a lifetime, the majority of us may find that we are better suite to a low carbohydrate diet.

A ‘low fat diet’ — even one restricted in calories — is high in carbohydrate, which drives up insulin levels. Insulin is a hormone that drives fat into storage (i.e., into fat cells) and stimulates hunger. A low carbohydrates diet, on the other hand, allows insulin levels to remain low and fat stores to be burned in the context of reduced hunger and cravings.

Insulin, which goes up in the blood when we eat carbohydrates, turns off fat oxidation and stimulates fat storage. And when we stop eating lots of carbs and our insulin levels fall, the opposite happens; fats come out of storage and become the body’s primary fuel.