Rapid Weight Loss vs. Slower Body-Composition Changes

Is there a superior way to change our bodies for climbing performance?

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You wouldn’t be wrong if you believed it’s advantageous to be light for
performance rock climbing—we all know it’s helpful to feel like you’ve slipped through gravity’s fingers. But is there a hidden cost to rapidly losing weight? Moreover, is there a more advantageous and sustainable way to change body composition?

Physiological effects of rapid weight loss

When you lose weight, you lose mass. And when you lose weight rapidly (more than 1 to 2 pounds per week), you’re more likely to lose both main types of body mass: fat, aka adipose tissue, which is hormonally active but doesn’t require as much energy to sustain; and muscle, aka lean mass, which requires a little more energy. This occurs because extreme caloric restriction slows your metabolism—the body, in an energy deficit, now has fewer calories to use (as well as less mass to fuel), and so reacts accordingly by conserving energy. This is basic metabolic balance.

Aside from rapid weight loss making you feel lethargic, another way the body decreases energy output is by metabolizing metabolically demanding tissue—i.e., muscle. This typically occurs to some extent regardless of weight loss; however, in times of fasting, when glucose and glycogen have been used up, the body will turn to amino acids (protein building blocks from the muscles) to make glucose in a process called gluconeogenesis. This muscle loss not only makes weight loss unsustainable, but can lead to diminished power and a higher chance of injury.

Unsustainable weight loss: Upsetting the metabolic scales


  • Age: 26 
  • Height: 5’8”
  • Weight: 160 pounds
  • Build: Fit, healthy balance of muscle and body fat

Bob has been climbing for six years, and hit a grade plateau at about year four around V7/V8. Rocky Mountain National Park bouldering season ramps up in about two months, so Bob decides to lose 15 pounds in hopes of sending harder. Each day, he’ll eat: 1 low-calorie protein shake + 1 low-carb, low-fat protein bar + a big, strictly vegetable salad with 4 ounces of lean chicken, dressed with lemon juice. He starts a 4x per week climbing, 3x per week running, and 2x per week lifting regimen with the goal of amplifying his caloric deficit.

After 8 weeks on this regimen, Bob hits his target weight. Throughout, he experiences drastic hunger, but remains committed. He notices more frequent muscle cramping and interrupted sleep, but he’s seeing gains at the gym, and so persists. After week eight, Bob heads into the alpine to try a V9, which goes down after a few weeks. He feels light, but not particularly energized; he can muster up power, but not always at optimal capacity. After sending, he tries another V9. In the meantime, Bob resumes eating the same foods and quantities as before his regimen—about double the calories per day. His low-calorie diet was leaving him too hungry to perform on the boulders, and he was bonking on the hike.

Over the next four months, Bob gains back about 17 pounds despite eating healthily and staying active. He’s happy to have sent V9, but feels frustrated that he’s now heavier than his original starting weight, and that he feels less powerful.

As Bob quickly learned, you not only get hungrier when eating less and exercising more, but your metabolism also slows. So, sure, Bob got down to “V9 sending weight,” but his sending window only lasted a couple of weeks—because, as discussed, rapid weight loss with no emphasis on losing fat while retaining muscle is often not metabolically sustainable.

Indeed, weight regain after weight loss is so common that research has quantified the body’s drive for more food, estimating that for every two pounds of weight loss, hormonal signaling prompts us to eat 100 more calories per day1. We saw this with Bob, as his hunger cues grew stronger than he could resist past eight weeks. This is the body trying to balance the metabolic scales. In fact, a commonly accepted statistic is that 80 percent of people who lose 10 percent of their body weight will regain that weight. Moreover, many people’s hunger cues become aggressive after bouts of rapid weight loss, and it’s not uncommon to experience cravings to eat in quantities surpassing your intake while dieting.

Sustainable weight loss: Balancing the metabolic scales


  • Age: 35
  • Height: 5’5”
  • Weight: 130 pounds
  • Build: Fit, healthy balance of muscle and body fat

Sarah has been climbing for 15 years and has a trip to the Red River Gorge six months out during which she wants to climb her first 5.13a. Psyche is high, but Sarah realizes that she’s in it for the long haul, and wants to dial in the many aspects of her lifestyle that will support getting into better shape.

Sarah started by cutting out alcohol and processed carbs, while oscillating between 3 to 4 light, lean-protein-containing, whole-foods-based meals per day. She also began to focus more on nutrient timing, ensuring that most of the high-carb, whole foods she consumes are within 30 minutes of training sessions. She also cut back on bars and high-sugar sports drinks, while adding in more electrolyte-infused water and pre-made, lean-protein-centric meals with ample vegetables. Protein shakes are used as needed after training. While precise about her eating, she is not restricting calories.

Sarah prioritizes getting 6 to 8 hours of sleep, especially around intense training days. Each week, she climbs at least 3 days, with a focus on endurance on one day and fingers the other two. As she goes, she listens to her body’s feedback and modifies accordingly. Over this six-month period of precise fat loss with muscle-maintenance nourishment, Sarah loses 11 pounds, most of which is fat. She feels powerful and light, and sends her goal routes at the Red. Sarah is able to sustain these changes throughout the year, and because many of them are lifestyle based, continues to see subtle improvements in body composition and performance, even as she become slightly less precise in her eating.

How focusing on body composition works

As Sarah learned, the way to sustainably reduce body weight is by focusing on body composition—losing body fat while maintaining lean body mass. Rather than being a starvation slog, the process can instead be enjoyable, and yields performance gains, more energy, (often) increased power, and less chance of an injury. The only “problem” is that prioritizing the maintenance of lean body mass while losing weight, which really ends up being fat, requires longer-term commitment. It requires changes around patterns and habits, which doesn’t cater to the typical American get-fast-results mindset.

So, how and why does focusing on body composition actually work? Well, first off, this nourishment pathway supports metabolism, as it leaves you with more energy-requiring muscle. (Note: Muscle only requires slightly more calories to maintain than fat, but longitudinally, those extra calories are beneficial.) As we saw with Sarah, this was best accomplished with a high-protein, whole-food-based diet (see below, as well as In addition to getting adequate lean protein, there are other dietary pillars that sustainably shift body composition: consuming fiber-rich carbs, eating plenty of greens, fresh fruits, and vegetables, avoiding processed foods, and staying hydrated. Meanwhile, factors like age, hormone dominance (sex hormones impact many biological functions, many of which impact body composition), elevation and geography, food preferences, activity levels, health conditions, sleep status, work, social, and cultural environments, genetics, and even your goals factor in as well.

Long story, short: If you want your body-mass reduction to be sustainable, then it’s more about the type of mass you lose than the amount. To be clear, I’m not encouraging you to go out and gain tons of muscle so that your metabolism gets faster. Nor am I suggesting that we could all stand to lose weight. However, because weight loss is a frequent conversation amongst climbers, let’s make sure we’re nourishing to optimize our climbing goals, fitness, and overall resilience.

The Protein Connection

A 2018 review in the journal Nutrients demonstrated that compared to other calorically restricted diets, a “high-protein diet” (at least 25–35 percent of your daily calories coming from protein) catered to losing more fat mass and preserving more lean mass than all of the other fat-loss macro ratios. This is no surprise, as muscle requires amino acids from dietary proteins to be synthesized. Likewise, protein is the most thermogenic macronutrient, which means proteins (aka amino acids) require energy to digest and absorb. Moreover, research has established that people with higher-protein diets trend toward consuming fewer calories, likely because protein consumption stimulates the “I’m full” hormone, leptin.

Alyssa Neill, registered dietitian and owner of Nourishment Nutrition, lives, works, and plays in Colorado. Find her online @nourishment_nutrition or @alyssa_neill.


  1. Goodman, B. (2016, October 14). Research Sheds Light on Why People Who Lose Weight Gain It Back.