High Fat Diet=Better Endurance?

I turned 33 on Sunday, and because we were having torrential rain, we decided to go to the National Aquarium. We’ve had tickets for a few months, but were waiting for a rainy day. And boy was it Sunday. We also went to Little Italy and to a fantastic little Italian Bakery, Piedigrotta. Piedigrotta’s owner, Carminantonio, was the supposed creator of Tiramisu, 40 years ago in Naples, Italy.

I thought about trying it, but since I don’t like coffee, and the lady fingers in Tiramisu are soaked in coffee liquor, decided against it. But we hear that it’s to die for. We did partake in splitting a shared meal. We got to chose 5 things on the lunch menu. And as you can see, it was a lot. We chose, vegetarian lasagna, pappardelle, frittata, gnocchi, and steamed veggies. It was all delicious! And full of both carbohydrates and fats, which is the topic of this blog.

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I’ve heard a lot recently about a resurgence in people thinking that they need to eat more fat and less carbs, in order to burn more fat as fuel. This is true to a degree, but I’ll explain why it’s not in your best interest as an endurance athletes. First, let’s look at our stores. Our carb stores are limited, vs our fat stores are abundant. In our liver, we only have about a 2 hour reserve of glycogen. When tapping into our fat stores, it’s close 10,000 calories worth. We could ride a long time on that. Unfortunately we use a mixture of fat and carbs while exercising. The harder you go, the greater the percentage of carb being used. The slower you go, the greater the percentage of fat being used. You’ll almost never use 100% of either at any one point though.

We studied quite a number of trials from the 20’s till today. I’ll go over the results of some of the studies, to show you where we have come from and where we are today.

Trial 1:

In the 20’s-40’s, experiments with high fat diets started to emerge. Scientists wondered, is there a way to utilize more fat as fuel, since we have a limited supply of glycogen? The studies placed athletes on a high fat/low carb diet for 3 days. Then, they placed them on a high carb diet for an additional 3 days. During the first 3 days, the athletes drove their muscle glycogen levels down, and felt tired, sleepy, fatigued and dizzy. Even in submaximal exercise (easier), they felt terrible. The following 3 days of high carbohydrate eating relieved these symptoms.

There was little research done in the 50’s-60’s.  Enter the 70’s and 80’s, and in came books like the Zone Diet. 40:30:30, or 40% carb, 30% protein, 30% fat.  This was a fad diet done by a few athletes, who turned it into a sports diet. The diet was meant to increase fat burning, increase endurance and decrease body mass. There wasn’t any research done, just anecdotes from athletes, which doesn’t qualify as scientific. This diet I consider to be one of someone who is more in their off season, not an athlete competing currently.

Trial 2:

1990’s-Old carbo loading premise. The athlete trains most of the year on a high carbohydrate diet, then one week before a major event, undergoes a 5 day period of fat adaptation, followed by 24-36 hours of a high carb intake to restore muscle and liver glycogen. This did allow athletes to use more fat as fuel, but not very practical. Eating a generally moderate to higher amount of carb just generally is considered to be best overall. For moderate to heavy exercisers, 7-10g/CHO/kg is a good start.

Trial 3:

2000-2010-multiple studies were done where athletes (highly trained cyclists and triathletes) were put on a one week HF (high fat) or HC (high carb)  diets with a 3 week wash out in between. They used the same athletes so they could compare the athletes results. They did 5 days of either HIT, long distance or hill work, followed by a rest day and both groups refueling with carbs and then a TT day. Results- muscle glycogen levels super-compensated in HF diets and HC diets. This was the first study to show spared muscle glycogen stores and higher fat oxidation in HF diet. Burke LM et al. J Appl Physiol 89:2413-2421, 2000

Trial 4:

Same study design as trial 3 although this time they increased the exercise time to 4 hours at 65%. Previously it was 2 hours long. This study showed higher rates of fat oxidation in HF diet and sparing of carb, the only downside was the HF athletes felt higher rates of perceived exertion then the HC.  But still, This seems pretty good right? We do want more fat oxidation and more sparing of glycogen, so far so good. Carey Al et al. J Appl Physiol 91:115-22, 2001

Trial 5:

Havemann L et al. J Appl Physiol 100:194-202, 2006

100km bike race, with regular intervals of bouts of 100% effort at 1km and 4km. Now under conditions where we are asking athletes to sprint, interspersed with steady state exercise, the fat adapted athletes were not able to put out as much power as athletes on higher carb diets. We learned that the muscles did burn more fat, but it also diminished the muscles ability to burn carb. So, fat adaptation is an impediment to utilizing carb.

Here are some general takeaways:

*high fat diets put the brakes on the body’s ability to use and oxidize carb. Not advantageous for athletes.

* the failure to find clear evidence of benefits to prolonged exercise at steady state, so we can delete fat-loading and high fat diets from the list of ergogenic aids for endurance athletes. “Louise Burke.”

So, the recommendation is some training down in a “low” carb state, while the majority should be done with carbs available.

So even though eating a high fat diet did allow athletes to spare glycogen and utilize more fat at fuel, there was no performance benefit seen long term. In fact, athletes were inadvertently shutting off their bodies abilities to utilize carbs, thus not allowing for performance gains.

In the next blog or two, Ill cover the benefits of training in a glycogen depleted state, or training “low.” As we could see today, there is definitely some benefit, just not in doing this type of diet full time.













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