Written by Eric Trexler
As we all know, body composition is a critical factor in many sports. Whether you’re going for a bodybuilding pro card, dropping fat to improve your speed, or dropping a weight class to seek out that record-setting squat, effective weight loss strategies will be key to your success.
A few months ago, I published a paper in the Journal of the International Society of Sports Nutrition (20). The paper was a literature review discussing the metabolic consequences of dieting, with an emphasis on how this literature pertains to athletes. If you read the paper and you’re a person with somewhat “normal” interests, you were probably bored to tears. So, the purpose of this article is to briefly summarize that huge wall of text in JISSN.
What is metabolic adaptation?
As JTS readers are well aware, the human body is resilient. You may have noticed that you’ve been able to add more and more plates to that bar on your back, despite the rigorous stress you’ve been putting your body through day in and day out.
When people talk about obesity, you sometimes hear about the thrifty gene hypothesis. The general idea is that humanity evolved to favor a genotype that allows us to store excess calories as fat, primarily as a survival mechanism. Essentially, we’re able to save up energy during times of feasting, just in case we encounter a famine later.
I like to think of metabolic adaptation as the other side of the thrifty gene hypothesis— instead of talking about what happens during the “feast,” metabolic adaptation addresses the “famine.”
During weight loss, two things happen: We impose a caloric deficit, either by increasing exercise or decreasing food intake, and we begin to lose body mass (hopefully most of this is fat mass, rather than lean mass). These are both indicators that energy supply is low, and the body adapts accordingly. In short, these adaptations may include (13, 20):
Increased mitochondrial efficiency (less calories burned to produce the same amount of ATP) (1, 7)
Decreased energy expenditure (metabolic rate) (5, 17, 18)
Elevations in hormones that promote catabolism and hunger, with decreased hormones that promote anabolism, energy expenditure, and satiety (15, 19)
What are the effects of these adaptations?
As you can imagine, these adaptations directly oppose your weight loss goals. Changes in mitochondrial efficiency and energy expenditure decrease your energy deficit, which slows weight loss. Further, the hormonal changes make it difficult to retain lean mass, threaten energy levels and general mood state, and increase hunger. One particularly unfavorable result pertains to the sex hormones; many natural male bodybuilders encounter symptoms of low testosterone late into contest prep (14, 19), and amenorrhea is commonly experienced by female athletes (10).
The effects of these adaptations also extend beyond the weight loss phase. Let’s say you made it down to that weight class you were shooting for, or you’ve achieved a stage-ready level of body fat.
Even after you’ve lost the weight, research has indicated that many of these adaptations persist as you try to maintain your new body weight (12, 17). These adaptations, which have decreased your metabolic rate and increased hunger, also set you up for a huge rebound. If you don’t practice some restraint after the diet, rapid weight regain is common.
Further, research has shown that the weight gained is this period is preferentially stored as fat (21), and that adipocyte hyperplasia (the addition of new fat cells) may occur (9). This can lead to a phenomenon known as post-starvation obesity (21) or body fat overshooting (6); in this scenario, the dieter actually regains more fat than they lost during the diet. Ultimately, this diminishes the progress made throughout the diet, and makes future dieting attempts more difficult.
Common misconceptions about metabolic adaptation
Metabolic adaptation has become a fairly popular topic of discussion amongst fitness coaches and competitors. As such, a number of common misconceptions have surfaced. A few of these misconceptions include:
1. Metabolic adaptation can make weight loss impossible, or can make you gain weight despite a caloric deficit
Metabolic adaptation does not refer to some supernatural circumvention of the laws of thermodynamics— these adaptations simply serve to decrease energy expenditure. So, the energy deficit becomes smaller, and weight loss may eventually stall as energy expenditure approaches energy intake. At this point, weight loss can continue if more exercise is added, or if caloric intake is reduced. But this becomes very tricky when exercise volume is already high, and caloric intake is already low. In some cases, you do reach a limit where it’s no longer advisable, practical, or healthy to continue making extreme adjustments.
2. These adaptations are a dire problem
These are adaptations that naturally accompany weight loss and address the “energy crisis” your body is facing in a caloric deficit, especially when you start to become very lean. A really dire problem would be if these adaptations didn’t occur, and the human body was more susceptible to starvation. If that were the case, our evolutionary history might tell a slightly different story.
3. These adaptations are indicative of improper dieting
Again, this is not 100% true. To some degree, these adaptations are to be expected with calorie reduction and weight loss. Even with the most optimized weight loss strategies, you will still expect these adaptations to occur to some extent. However, it is likely that they are exacerbated by improper strategies, so they can likely be attenuated by a more ideal approach to weight loss.
What can be done to avoid these adaptations?
Unfortunately it is unlikely that these adaptations can be avoided entirely. However, you can likely minimize them by employing proper dieting techniques.
Obviously, sufficient protein is important. It has the highest thermic effect of any macronutrient and is highly satiating (16); further, it will assist in the retention of lean mass and metabolic rate (11). The same can be said for participation in a structured, well-designed resistance training program (2). But you’re reading an article on the JTS website, so you’re probably taking care of those already.
Theoretically, the magnitude of these adaptations is likely related to the size of the energy deficit (20)— a larger deficit signifies a more urgent energy crisis. So, it is advised to impose the smallest possible deficit that yields appreciable weight loss, and to establish a relatively slow rate of weight loss (3). When weight loss begins to stall, make modest, conservative adjustments to increase the energy deficit, and approach the diet in a step-wise fashion with incremental, periodic adjustments.
Unfortunately, cardio often becomes a necessity when trying to achieve very low body fat. However, as a general rule, it may be best to keep cardio as minimal as possible throughout the weight loss phase. Not only can cardio potentially cut into your recovery from resistance training, but the interference effect of concurrent training may be counterproductive. When cardio is necessary, it may be best to avoid higher-impact modalities, long durations, and low intensities; a mix of moderate intensity cardio and high-intensity intervals on a stationary bike are solid choices (22).
Periodic carbohydrate refeeds are currently very popular in the world of physique sports. Theoretically, they may help to influence metabolic rate and satiety by temporarily elevating leptin (4), but more research is needed on this topic. Reverse dieting is another popular strategy employed by physique athletes. While there is little relevant data on this strategy, it could theoretically help with maintaining weight loss. While a bodybuilder should not aim to stay at stage weight for an extended period of time, this strategy could help competitors stay within striking distance during their offseason, and is likely to prevent body fat overshooting in the post-diet period. For the general population, reverse dieting may help them maintain a large percentage of their weight loss, but this is speculative and research on the topic is needed. It is important to emphasize that reverse dieting does not mean you need to keep a caloric deficit beyond the intended weight loss period— it simply refers to gradually increasing calories, as opposed to a massive, drastic caloric surplus.
For more practical strategies for weight loss, refer to a recent (excellent) paper by Helms, Aragon & Fitschen (8).
There are certain metabolic adaptations that accompany energy restriction and weight loss. These adaptations, which are likely survival mechanisms to avoid starvation, generally serve to increase efficiency and reduce the caloric deficit. While metabolic adaptation is not some dire, perilous occurrence, it certainly opposes weight loss goals. Although metabolic adaptation is not entirely avoidable, a well-planned approach to training and nutrition can likely minimize these adaptations and promote more successful weight loss. By employing sound weight-loss strategies, you can lose the weight more effectively, increase the likelihood of maintaining weight loss, and set yourself up for improved body composition and performance down the road.
About the author:
Eric Trexler is a strength coach, powerlifter, and natural bodybuilder, and serves as the Director of Research and Education for INOV8 Elite Performance. He is also a graduate student and active researcher, conducting exercise and nutrition research at the University of North Carolina at Chapel Hill.
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