We've Known It For At Least 75 Years
Here's an excerpt from a diet and nutrition book I found at a book sale:
"Practically speaking, exercise alone doesn't reduce weight dependably... Suppose you are of average weight and you take a brisk two-mile hike on level ground. You figure pridefully that you have burned up a few ounces of fat. The sad truth is that your two-mile hike consumes an excess of a mere 115 calories, which are easily replaced by a mild snack consisting of three graham crackers."
Here's the twist: The book from which that excerpt was taken was published in 1941, right about the time the U.S. was declaring war on Japan for attacking Pearl Harbor.
That means that we've known for at least 75 years that exercise doesn't really do much to reduce weight, yet celebrity TV trainers and gym trainers continue to hoodwink clients into thinking that all that jumping and jiggling huffing and puffing is going to svelte them right down to fashion-model size.
And even those of us who are supposed to know better about fat loss will hop on an exercise bike at the first hint of impending roly-polyness. It's all largely a delusion because true fat loss happens mostly as a result of calorie deprivation (eating less), improved insulin sensitivity, and, theoretically at least, modified gene expression.
It turns out, though, that exercise might actually play a bigger part in fat loss than we thought, but only exercise done at a certain time and under certain conditions, and it has to do with modified gene expression that might not be as theoretical as we thought.
We've long known that in the short term, exercising on an empty stomach burns more fat than exercise done on a full stomach when there are nutrients in the blood to fuel our muscles.
Even so, the fat loss was so negligible that it hardly made fasted training worth the effort. What we didn't know, though, until recently, is that fasted exercise alters gene expression of certain enzymes and in the long term can "train" your body to break down fat tissue, making fasted exercise a viable fat-loss method.
British researchers at the University of Bath found 10 men with an average waist size of about 41 inches give or take about 4 inches, to jog for an hour at moderate intensity (60% of VO2 max). First they ran on an empty stomach. On another occasion they ran two hours after eating a breakfast of 650 calories (kilocalories).
As expected, the runners burned 20 fewer grams of carbs and 7 grams more fat while fasted than they did when non-fasted. Nice, but no real game changer as far as losing an appreciable amount of body fat. However, the fasted running activated a series of fat-burning genes that code for the following fat-burning enzymes:
- PDK4: An enzyme that causes cells to burn more fat than glucose.
- ATGL: An enzyme that disassociates fat cells.
- HSL: Another enzyme that disassociates fat cells.
- FAT/CD36: An enzyme that helps muscle take up long-chain fatty acids.
- IRS2: An enzyme that plays a part in insulin secretion.
The more these genes are activated, the better the body gets in breaking down fat.
Dylan Thompson, one of the authors of the study, explained in a press release that, "Adipose tissue often faces competing challenges." After a meal, adipose tissue "is busy responding to the meal and a bout of exercise at this time will not stimulate the same [beneficial] changes in adipose tissue. This mean that exercise in a fasted state might provoke more favorable changes in adipose tissue, and this could be beneficial for health in the long term."
Calorie deprivation remains the best way to purge body fat, but fasted exercise, most easily done first thing in the morning, could possibly turn on various genes that affect fat-regulating and fat-burning enzymes.
That means that an early morning jog, bike ride, or session on the Nordic Track could not only burn some fat, but set you up so that your system becomes more efficient in burning fat in general, which would make dieting more effective and presumably less painful.
This info might also be useful for bodybuilders who want to burn fat but worry about burning up muscle at the same time. Bodybuilders could do some "cardio" first thing in the morning in a fasted state, and then continue to eat for muscle during the day.
While they wouldn't be in a calorie deficit during the day, the fasted cardio might train their bodies to break down body fat regardless.
- Cooley DG. The New Way to Eat and Get Slim. Wilfred Funk Inc. New York, 1941.
- Chen YC et al. Feeding Influences Adipose Tissue Responses to Exercise in Overweight Men. Am J Physiol Endocrinol Metab. 2017 Jul 1;313(1):E84-E93. PubMed.
- American Physiological Society (APS) To eat or not to eat (before exercising): That is the question. Science News. April 6, 2016.