Evidence at a glance
Each entry rates a specific claim or decision, not an ingredient, habit or product as a whole. The index launches with 37 claims drawn from published Fitness World investigations and expands as new evidence-led work is published.
Find the right evidence page
Looking for something else? Choose the page that fits your question:
- Supplement Evidence Index — check supplement claims by specific outcome and evidence strength.
- Product Evidence Reviews — see whether products and devices live up to their marketing claims.
- Evidence Standards — understand the rules Fitness World uses to rate research and claims.
- Evidence Projects — follow reader-supported investigations from question to published result.
- Evidence IQ — test how well you can spot what health evidence really supports.
Find the specific claim or outcome.
Filter by topic or evidence strength, then reveal results six at a time.
Evidence strength summarizes the quality and consistency of the research. Fitness World verdict summarizes what that evidence means for the specific claim. A moderate evidence rating can still support a claim with important context or limitations.
Creatine for Strength and Muscle: Evidence Guide
Creatine is one of the better-supported sports supplements for strength and lean-mass gains when paired with resistance training.
Protein for Muscle: How Much Is Enough?
Adequate protein supports muscle growth with resistance training, but benefit does not increase indefinitely with higher intake.
Do You Really Need 10,000 Steps a Day?
Research does not show 10,000 steps is a biological threshold required for health benefit.
Walking After Meals: Effects on Blood Sugar
Short post-meal walking can reduce the immediate post-meal glucose rise compared with remaining sedentary.
Magnesium for Sleep: What the Evidence Really Shows
Magnesium is widely marketed for sleep, but the evidence is not strong enough to treat it as a reliable sleep solution for everyone.
Seed Oils: What Human Studies Show
Current evidence does not support treating common seed oils as inherently toxic or automatically inflammatory.
Do Omega-3s Actually Work? What the Evidence Shows
Omega-3 evidence varies by outcome. Benefits are clearer for some uses than for broad wellness promises.
Does Morning Light Actually Help You Sleep Better?
Light is a strong circadian signal; timing and consistency matter more than vague advice to simply get sunlight.
Can You Build Muscle After 50?
You can build muscle after 50. Start where you are, progress what you can measure and think in years rather than weeks.
Strength Training After Menopause: What Actually Matters?
Strength training remains one of the highest-value habits after menopause for preserving strength and capability. Start with a manageable program and progress it rather than chasing a menopause-specific workout gimmick.
Walking vs Strength Training After 40: Do You Need Both?
For healthy aging, walking and strength training are complementary, not interchangeable.
Is Two Strength Workouts a Week Enough?
Two strength workouts a week can be an effective long-term baseline. Quality and progression decide whether they work.
Whey vs Plant Protein: Which Is Better?
Whey is a strong default for muscle, but plant protein can work well. The best choice is the one that fits your diet and reliably helps you meet protein needs.
Protein Powder vs Food: Do You Actually Need a Supplement?
Use food as the foundation. Protein powder is worthwhile when it solves a real convenience, appetite or intake problem — not because powder builds muscle differently from adequate high-quality dietary protein.
Creatine Monohydrate vs Creatine HCl: Which Should You Choose?
Creatine monohydrate wins on evidence and usually on price. HCl is an alternative format, not a proven upgrade.
Are Collagen Powders Worth It?
Collagen powder can be a reasonable optional product, but the evidence is more mixed than the marketing suggests and it should not replace higher-quality protein for muscle.
Greens Powders: Useful or Overhyped?
For most people, greens powder is optional convenience, not a substitute for fruits and vegetables. Spend first on a varied diet; judge any powder by transparent ingredients, dose, testing and a specific reason for using it.
Are Electrolyte Powders Worth It for Everyday Use?
Electrolyte powders are worth it for specific hydration problems. They are usually unnecessary as an all-day wellness ritual.
Are Cold Plunges Worth It?
Cold plunges can be useful for short-term recovery and preference, but the broad wellness claims outrun the evidence.
Are Red-Light Therapy Devices Worth It?
Red-light therapy is not pseudoscience, but neither is every red-light device evidence-based. The product and the claim have to match the research.
Sleep Trackers: How Accurate Are They?
Sleep trackers can be useful for self-monitoring, but the stage-by-stage precision is easy to overinterpret.
Is an Oura Ring Worth It for Sleep?
Oura can be worth it as a behavior-feedback tool. It is not a clinical sleep test and it is not necessary for good sleep.
Fitness Watch Calories: How Accurate Are They?
Fitness-watch calorie estimates are useful-looking numbers, not laboratory-grade measurements. Do not build a diet around them.
Heart Rate Variability: Is Your Wearable’s HRV Score Useful?
Wearable HRV can be useful for trends under consistent conditions. It should not be interpreted as a stand-alone measure of health or readiness.
Fiber Supplements vs Food: Which Makes More Sense?
Use food as the foundation and fiber supplements as targeted tools. The supplement does not make the food obsolete.
Psyllium vs Chia Seeds: Which Is the Better Fiber Source?
Psyllium has the stronger case for targeted fiber supplementation; chia makes more sense as part of food.
Prebiotics vs Probiotics: What’s the Difference, and Do You Need Either?
Prebiotics and probiotics are different tools. Neither is a universal gut-health requirement.
Magnesium Supplements vs Magnesium-Rich Foods
Magnesium-rich foods are the default source. Supplements are targeted tools, not upgrades to food.
GLP-1 Supplements: Which Marketing Claims Should You Question?
There is no evidence-based reason to treat an over-the-counter “GLP-1 supplement” as a substitute for prescription GLP-1 therapy.
Lemon Water and Metabolism: Evidence vs Hype
Lemon water is hydration with flavor. It is not a proven metabolism booster.
Creatine and Hair Loss: What the Research Can — and Cannot — Tell Us
The hair-loss concern around creatine has circulated for years. Direct evidence now gives the claim a much clearer test.
Ashwagandha for Stress: Evidence and Safety
Ashwagandha is marketed as a stress solution, but the evidence is more specific—and less universal—than the advertising often suggests.
Melatonin for Adults: When Does It Help Sleep?
Melatonin is one of the most familiar sleep supplements, but its usefulness depends heavily on what sleep problem you are trying to solve.
Curcumin for Knee Osteoarthritis: What Pain Studies Suggest
Turmeric and curcumin supplements are heavily marketed for joints. The evidence is more encouraging for knee osteoarthritis than for vague “inflammation” promises.
Can You Trust the Sleep Stages on Your Watch or Ring?
Consumer wearables can be useful for sleep trends, but “deep sleep” and “REM” estimates are not the same thing as a sleep-lab measurement.
How Accurate Is Your Smartwatch Step Count?
Step counts are one of the more useful wearable metrics, but different devices and wear locations can still disagree by hundreds—or more—steps per day.
How Long Should You Rest Between Sets After 40?
Short rests make workouts feel harder. Longer rests can help preserve performance. The best choice depends on whether the goal is strength, muscle or simply getting the session done.
Evidence strength can vary by population, dose, outcome and study design. Fitness World uses these labels to summarize published research for education; individual health decisions may require a qualified professional.