This post is actually a response to some recent publications that have compelled me to hit the keyboard. As every participant in Project JACKED is undergoing amazing progress with health enhancement, body composition improvement, fitness, and energy levels, we have to take a look at America’s preoccupation with this one big (couldn’t resist) thing: weight loss. My opinion, and that which is validated by the literature, is that weight loss is not a separate entity in wellness but merely a reflection of the attainment of normalized or optimized health. However, it is our supreme cultural focus, and I feel I must address it.
Losing weight is achieved by balancing hormone levels and utilizing stored bodyfat for fuel. How this happens is based upon several factors. The traditionally-held mechanism for fat loss is the thermodynamic equation of caloric expenditure: calories in (consumed) versus calories out (burned). In this paradigm, when attempting to lose weight, we try to create a subtle caloric deficit and over time the body theoretically burns up fat to make up the difference in demand created by our basal metabolic rate plus activity requirements. There is a place for this theory but it really is secondary to what is known as the endocrine (hormonal) theory of weight loss. When our hormones are in proper balance, and our health and stress levels are optimal, the body can more easily be in a fat-burning, as opposed to a fat-storing, mode. If we only look at calories, then the argument that 2000 calories of marshmallows would have the same nutritional effect as 2000 calories of broccoli would have merit. Even a 5-year-old knows this just isn’t true.
And then we get to exercise. Or, more specifically, the use of exercise as a tool to burn off fat. Honestly, your fork is a far better tool in weight loss than your dumbbell or running shoe (and the dumbbell may be superior to the running shoe in a comparison regarding weight loss). I think we all recognize that exercise, of the correct types and amounts, provides us with many health benefits. But it really is only one part of the weight loss equation. This becomes of particular concern when we look at the effect of exercise on appetite.
A study conducted at Loughborough University in Great Britain, recently published in the Journal of Endocrinology, and also profiled in a New York Times Well article, examined the effect of exercise duration and intensity on hunger in 18 male treadmill runners. Study subjects were divided into two groups. One group, on different days, was monitored while performing the following: sitting quietly for several hours, jogging for 55 minutes at 52% VO2max, and running for 36 minutes at an effort level of 75% VO2max. The other group performed the same sitting protocol but also ran trials of both 45 and 90 minutes at 70% VO2max. Subjects were monitored for levels of grehlin, the hormone most associated with hunger, and were also subjectively queried about their appetites. Of perhaps greatest significance, and certainly no surprise to most of us was the result that grehlin levels and reported hunger were lower in all exercise conditions as compared to the sedentary state, which is known to accelerate hunger and appetite, whether due to metabolic dysregulation, boredom, etc. But the results which occurred during the exercise conditions, and from which we may have a tendency to formulate extrapolations, cause me some degree of concern.
In the study, grehlin levels were suppressed with all forms of exercise but the response was greater in the longer duration (90’ @ 70%) and higher intensity (36’ @75%) groups. These results appear consistent with the methodology employed in the study but it is here where we need to use caution with interpretation. There is a potential for misunderstanding, both in the study’s conclusion as well as in the NYT article, that increasing both duration and intensity of exercise can have an appetite-blunting, and potentially, a weight loss effect. To blatantly make that assumption would be inconsistent with the physiology of exercise and metabolism.
First, let’s look at a few aspects of the study before we come back to this point in the discussion. This was a small study, looking only at male runners, with a small number of trials. The subject’s level of fitness, dietary habits, and metabolic rates of fat oxidation during exercise were not controlled for in the methods. These are all significant factors which can profoundly affect responses to training, and certainly fluctuations in key hormone levels such as grehlin. Also, all of the exercise conducted was technically in the low-to-moderate range with respect to intensity. True high-intensity training happens at effort levels of 90% and greater, and are actually better represented by sprinting, heavy weight lifting, and short-duration bouts lasting from a few seconds to a few minutes, at most. By this definition, high intensity exercise simply cannot be sustained for the exercise durations used in this study. To be fair, neither the authors of the original study nor that of the NYT article make this suggestion, but I believe the uninformed reader could easily be mislead toward such an assumption.
Exercise can be a useful tool in many of our wellness endeavors. But while there may be similarities, how we apply it for weight loss, health enhancement, or fitness improvement can be slightly different. If we get back to the recognition that burning off excess bodyfat is the underlying premise of weight loss, we really don’t burn that many extra calories during an exercise session in isolation. I’m sure you’ve all seen some of those advertisements that suggest you have to run on a treadmill for 50 minutes to burn off just one cookie, or something like that. What exercise actually does for our weight loss pursuits is it stimulates, or revs up, our metabolisms, and if we are intelligently applying this stimulus in the presence of ideal dietary and lifestyle factors, we “teach” our metabolisms to seek and utilize stored bodyfat for energy, and to eliminate the undesirable excess amounts of this adipose tissue. Exercise is a stimulus, or a stressor if you will, that sends messages to our bodies and it works in conjunction with what we eat, how we sleep, etc.
Brief, high-intensity exercise, such as a 10’ high-intensity interval protocol (which involves bursts and rests), or a few sprints on a bike, or a couple near-max lifting sets, offer a hormone-stimulating, or hormetic, effect that increases testosterone, growth hormone, and lipase enzymes to increase fat burning. It also suppresses hunger, and improves insulin sensitivity. Think of when you’ve done that type of training, or even a chore like unloading a truckload of mulch for your garden, and ask yourself if you were hungry immediately (or even for an hour or two) afterward. No, you probably were not. Likewise, longer, easier sessions like a long walk or hike, or a jog for a trained runner, don’t actually increase hunger immediately either. Here’s why: Neither of those workouts cause a great degree of glycogen depletion in our bodies. Glycogen is our stored sugar for semi-sustained, high-energy bursts (almost like an emergency nitrous oxide switch, or a reserve jet fuel tank which we access and burn only during high demand that lasts longer than a few seconds, but which won’t last for too many minutes). When we do training that is either fairly high (let’s say ~89% of perceived max effort) for 5 minutes, or moderate-plus (I made that up, but let’s say ~84% of max) for 60 minutes, both those forms of training are known to be glycolytic, because we need to tap into that stored jet fuel (glycogen) to get the job done. The high intensity group in the Loughborough study performed at 75% VO2max, which correlates to approximately 85% max HR, but may not have exercised long enough to deplete significant glycogen.
So here is where I make the distinction. When training for weight loss, occasional, brief, very high intensity training, when done safely, is excellent for stimulating hormonal regulation of fat burning. And very, very easy workouts, even it they are of long duration, don’t create a sugar demand (and thus appetite) because they stay in an effort zone that relies primarily on fat oxidation (this varies per individual based on fitness level and metabolic fat-adaptation status). So, in all probability, the subjects in the aforementioned study did not appreciably get into glycolytic stages during their exercise bouts. However, the article did mention that the 36’ @ 75% group, employing the highest intensity used in this study, while not showing increased grehlin levels post-exercise, did report an increased perception of hunger following their workout. This could be an indication of a delayed response in the hunger cycle as well as other mechanisms driving feeding urges and perceptions. My position, which is not a mere opinion and is well-supported in current literature, is that if either the exercise intensity, and/or the durations were appreciably increased in the study we are discussing, ravenous hunger would have ensued across most participants.
And that gets into the problem concerning weight loss. If we exercise too hard for too long, our bodies perceive this as a stress, and in a protective instinct, they compel us to eat more food in response to the exercise. This is particularly true with respect to carbohydrates, which would be depleted by the glycolytic exercise, and the body will have a sincere desire to replenish those emergency stores. I call this “carb-eatback syndrome” and I’ve seen it hundreds of times, no thousands. This appears to be less true in the case of extreme fat-adaptation, or people following ketogenic diets, but this condition will exist amongst all hard-training humans. Volume and intensity with exercise, regardless of whether we are training for health, fitness, or weight loss, exist on a progressive slope which can be graphically represented by a diagonal line. The harder we work, the shorter it lasts, and vice versa. Just like a gas pedal.
So let me sum this up by saying that exercise is good for you and I highly recommend that you continue doing so, in the manner that is most safe and effective for your individual goals. Whenever I consult with clients, I always remind myself that each of us is unique and our practices need to be tailored individually. But generally, we should all recognize that increasing exercise volume and intensity, especially together, should be done carefully if at all and this may not be a valuable practice when weight loss is the goal.