The Weight-Loss Trap of Watts per Kilogram: Lose the Wrong Way and You'll Sell the Engine Along with It

The Allure and Trap of W/kg

Climbers and endurance athletes are extremely sensitive to power-to-weight ratio (W/kg)—at the same 300 W, the climbing speed difference between a 70 kg and a 62 kg rider is night and day. Thus, “losing weight to boost W/kg” becomes a powerful temptation. But this equation has a fatal blind spot: the numerator (power) and denominator (weight) interact with each other. When weight loss is done incorrectly, power (the numerator) drops along with it, sometimes even more than the weight does, and W/kg may fall instead of rise—you think you’re optimizing the engine-to-chassis weight ratio, but you’re actually selling off the engine along with it.

The Cascading Costs of an Excessive Energy Deficit

Overly aggressive dieting in pursuit of lightness easily slides into low energy availability and RED-S (see the RED-S article), a high-risk condition for climbers and weight-sensitive athletes that is often misread as “dedication.”

How to Cut Weight Without Selling the Engine

• Moderate the deficit: Use a mild energy deficit (small, sustainable rather than extreme dieting), with a slow weight-loss rate (a common safe reference is a very small percentage of body weight per week), preserving training performance and muscle.
• Raise protein: During weight loss, push protein higher (commonly ≥1.6–2.0 g/kg), reach saturation at each meal and spread intake across meals, paired with resistance training to protect muscle and power (see the protein and sarcopenia articles).
• Keep carbs strategically: Don’t cut carbs on high-intensity and race days (protect the numerator and adaptations); create the deficit mainly through non-critical periods and overall portion management rather than going fully carb-free (ketosis reduces economy and high-intensity output, see the carb periodization article).
• Timing: Schedule weight loss during the base phase/off-season; before races and during the racing season, energy should be sufficient and performance-focused—no aggressive weight loss before important events.

Don’t Just Stare at the Scale

Short-term body weight fluctuations are heavily influenced by glycogen, fluid, and gut contents (each gram of glycogen binds about 3 g of water). Use weight trends combined with performance (power, endurance tests) and subjective/health markers for a holistic assessment, avoiding over-dieting or misjudgment due to water fluctuations.

Psychological and Health Red Flags

An excessive obsession with being light can slide into disordered eating behaviors. If you experience amenorrhea/low testosterone, repeated injuries, declining performance, low mood, or anxiety around food, stop and seek sports nutrition and medical/psychological professionals—these are your body protesting, not a lack of willpower.

W/kg is a fraction, not just the denominator. Starving your weight down often costs you power, glycogen, hormones, and health all at once, making the fraction even uglier. Smart lightening is: a slow small deficit, higher protein, preserved key carbs, and placed in the off-season—keep the engine, then talk about weight.

Related Reading

• Climbing Weight Management: The Truth About W/kg and Healthy Weight-Loss Strategies
• Managing Weight and Power: Strategies for Maintaining Power During Weight-Loss Training
• Weight Strategies for Climbs: Evaluating the Real Benefit of Pre-Race Weight Loss on W/kg
• Weight Management for Climbers: The Relationship Between W/kg Ratio and Climbing Speed