Running on Fat …

Back in my marathon days (30+ years ago) I remember reading a prediction that it wouldn’t be long before women were beating the men over the magic distance of 26.2 miles. The logic was very simple, fat is an excellent fuel, fit women athletes carry more fat than fit men athletes therefore women would be better over long distances than men once they matched the men in training.

So far it hasn’t happened, fastest man – Eliud Kipchoge of Kenya 2:01:39 fastest woman Brigid Kosgei also from Kenya 2:14:04. Getting on for 10% slower.

At about 9 calories per gram fat is an excellent fuel trouble is for endurance sports the body is very happy burning glucose and glycogen even though they pack only 4 calories per gram. Stores of glycogen exist in muscle and in the liver amounting to about 600 grams. In ball park figures that’s about 2400 calories for a marathon requiring about 2600. A runner can expect to absorb 50 to 60 grams of glucose from the gut per hour which easily makes up the shortfall.

So fat burning doesn’t really get into the equation during an elite marathon. If it did even the thinnest male athlete has enough fat to go the distance.

Glycogen is king. Glycogen replenishment happens faster after a carbohydrate rich meal. What are the implications for the athlete following a keto diet? Depends who you ask. According to Harvey, Holcomb & Kolwicz the keto athlete is operating at a distinct disadvantage although it is an excellent diet for weight loss.

Dr Caryn Zinn on the other hand is more optimistic …

while Professor Asker Jeukendrup sums up what is known but leaves the question open. That article is well worth reading.

Fat oxidation rates are on average 0.5 grams per min at the optimal exercise intensity. So in order to oxidise 1kg of fat mass, more than 33 hours of exercise is required! Walking or running exercise around 50-65% of VO2max seems to be an optimal intensity to oxidise fat. The duration of exercise, however, plays a crucial role, with an increasing importance of fat oxidation with longer exercise.

There is no doubt that the reforming couch potato can successfully lose weight and burn fat at moderate rates of exercise on a keto diet. Fat around the middle is as much a handicap as lead in the saddle bags. VO2max is the upper limit of your ability to burn fuel a good measure of your fitness. More precisely it’s milliliters of oxygen consumed in one minute, per kilogram of body weight (mL/kg/min) at sustained maximum effort. In other words get the kilograms down and the VO2max goes up without any extra training.

Progress Report …

We are two weeks into the Low Carb diet. Gayle has been cooking up a storm. Some of the food is less than exciting but most is delicious. Some is quite exceptional given the inclusion of previously shunned fats.

We haven’t been able to bring ourselves to eat dead animals so have to be thoughtful about our protein, eggs and cheese are in after that it’s tofu and nuts. Ground linseeds help with the omega 3s. Vitamin B12 comes from a pill.

I was losing weight before starting the diet. Three kilograms in the three months since I bought the bike. Two more kilograms have gone in the past two weeks along with 2 inches off the belly. No cravings, hunger satisfied. Not a calorie has been counted. I’m drinking a lot and peeing a lot, sure signs of ketosis. My confidence is high.

It feels as though athletic performance has suffered a bit, perhaps more for Gayle than me. We have been able to keep up a pretty high volume (by our standards anyway) 343 km in the past 14 days. I skipped this week’s long ride in favour of a more modest distance. I think we are getting through that now as we start to burn fat as our energy source.

Every diet that I’ve tried has worked … for a while. The promise from this one is that it will go on working. We will see.