“It works for me.”—oh does it?
Does that new diet work? Does that supplement work? Should you eat carbs and/or protein pre-/post-workout?
There are two general ways to answer such questions: scientific studies or personal experience. Both approaches are flawed.
Grounding your dietary decisions in new scientific studies is unreliable because:
- It is almost impossible to get unbiased funding for well-conducted long-term studies with healthy, athletic subjects and precise control over consumption, lifestyle, activity, and further factors (e.g., adaptation to fasting or ketosis).
- Statistical averages don’t necessarily provide optimal guidelines for unique bodies with individual demands.
Grounding your dietary decisions in personal experience through trial-and-error testing, too, is unreliable not only because of cognitive biases, but also because it’s impossible to keep all other variables constant. When you want to know, say, whether a supplement works for you, you have to look at how your desired outcome variable changes in response to taking the supplement. The desired outcome variable could, for example, be increased strength performance, more muscle mass, shorter recovery time, elevated well-being, better skin condition, higher energy levels, or greater sex drive. While you look at how your desired outcome variable changes when you take the supplement compared to when you don’t, everything else in your life must stay constant. This, however, is impossible. Just ask yourself:
- Do you eat exactly the same foods and exactly the same amount of macronutrients every day?
- Do you always cook your food exactly the same way (duration, temperature, etc.) and is it always equally fresh (exact same amount of micronutrients)?
- Is there absolutely no variation in any drugs or other supplements you take?
- Are your sleep duration and sleep quality constant every night?
- Are all your workouts and workdays, which affect your energy balance, equally intense?
- Are your social and sexual life with all their stressors and stress relievers the same every day?
- Does the weather, which affects your hormones, always stay the same?
- Are your thought patterns always equally positive?
- Is your willpower momentum always equally positive?
Since you most probably can’t ever answer every single question with “Yes,” you can’t really claim that a certain supplement works for you. People often say, “It works for me,” when they give advice, even though they might not actually have solid reasons to believe that. They can’t even exclude a placebo effect. Usually people believe that something works for them simply because it agrees with their other beliefs; for coherence of beliefs allows them to develop trust.
Trust is the most crucial factor here, but how can you develop trust when you’re a critical thinker who knows about cognitive biases, confounding subconscious factors, and the problem of holding variables constant?
Here’s what I do:
- I try to be honest to myself.
- I reflect on cultural hype, marketing strategies (e.g., from supplement companies), new scientific findings, and recommendations (e.g., from fitness gurus) and on how they might have biased my mind.
- I study the basic scientific principles of human nutrition, physiology, cognition, motivation, and performance.
- I test every new dietary change for at least three weeks while doing my best to hold all other variables constant.
- I measure my desired outcome variable precisely.
Everybody should have some personal standard to fulfill before he claims, “It works for me.”