The Science
The Data
Men at optimal body fat (~15%) have the lowest all-cause mortality risk, while those at 40% body fat face nearly 3.5x the risk of dying from any cause. For women, the optimal range is around 20-25%, with risk rising sharply above 35%. A dose-response meta-analysis of 35 prospective cohort studies found that each 10% increment in body fat was associated with an 11% increase in all-cause mortality (HR 1.11, 95% CI: 1.02-1.20).[1]
Health risk by body fat percentage ranges
The Studies
Body fat percentage is not just a vanity metric -- it is a meaningful predictor of disease risk and longevity. The research on body composition and health outcomes is extensive and consistent.
- Direct Mortality Risk: Jayedi et al. (2022) conducted a systematic review and dose-response meta-analysis of 35 prospective cohort studies covering 923,295 participants and 68,389 deaths. They found that each 10% increment in body fat was associated with an 11% increase in all-cause mortality risk (HR 1.11, 95% CI: 1.02-1.20). The relationship was J-shaped, with the lowest risk observed around 25% body fat.[1]
- Superior to BMI: A 2025 study in the Annals of Family Medicine using NHANES data found that body fat percentage and waist circumference showed stronger associations with all-cause mortality over a 15-year period compared with BMI (P < .01 vs P = .05). BMI misclassifies muscular individuals as overweight and fails to identify "normal weight obesity" -- people with normal BMI but elevated body fat who face significantly increased risk of metabolic syndrome and cardiovascular disease.[2]
- Visceral Fat Drives Disease: A position statement published in The Lancet Diabetes & Endocrinology (Neeland et al., 2019) established that visceral adipose tissue is an independent risk marker of cardiovascular and metabolic morbidity and mortality. Visceral fat releases pro-inflammatory cytokines and free fatty acids that worsen insulin resistance and accelerate atherosclerosis, making it far more dangerous than subcutaneous fat.[3]
- Metabolic Syndrome and Insulin Resistance: Research shows that body fat percentage is a strong indicator of insulin resistance even in people with normal BMI. Kim et al. (2018) found that high fat / low muscle body composition was associated with significantly higher insulin resistance and metabolic syndrome prevalence, while individuals with normal weight obesity had six times greater risk for metabolic syndrome than those without.[4]
The Plan
GLP-1 Medications (Ozempic, Wegovy, Mounjaro)
GLP-1 receptor agonists are a class of medications originally developed for type 2 diabetes that have proven highly effective for weight loss. They work primarily through appetite suppression -- they reduce hunger and increase feelings of fullness, which in turn causes people to eat less, which in turn creates a caloric deficit and causes weight loss.
The key nuance is this: whether the weight you lose is fat depends on whether or not you are strength training. Without resistance training, a significant portion of GLP-1-induced weight loss can come from muscle mass, which is counterproductive to long-term health. Combined with the strength training protocol on this site, GLP-1 medications can be an effective tool for losing fat specifically while preserving or even building muscle.
GLP-1 use should not be stigmatized. For people who struggle with appetite regulation, these medications are a legitimate tool in the toolbelt -- no different from any other evidence-based intervention. The goal is improving your health metrics, and if a GLP-1 medication helps you achieve a healthier body fat percentage while you strength train to maintain muscle, that is a good outcome.
Supplements
Before taking any supplement, apply this framework:
- What metric is being measured? Identify the specific, measurable health outcome the supplement claims to improve.
- Are there studies tying that metric to a health outcome? Is there peer-reviewed research demonstrating that improving this metric actually leads to better health?
- How will you track your progress against that metric? Can you objectively measure whether the supplement is working for you?
For example, consider the multivitamin -- one of the most commonly purchased supplements. What metric is being tracked? Is there science tying that metric to a health outcome? For a multivitamin, the answer is no. Large-scale randomized controlled trials have consistently failed to show that multivitamin supplementation reduces the risk of cardiovascular disease, cancer, or all-cause mortality in well-nourished populations. People take them because it feels like they should be doing something, not because the data supports it.
Apply this framework rigorously to every supplement before spending your money. If you cannot identify the metric, the supporting research, and your tracking method, the supplement is not worth taking.
Protein
Apply the same framework. The metric here is muscle mass and strength, and yes, there is strong science connecting adequate protein intake to the body's ability to maintain and build muscle tissue. So protein intake matters -- but far less than most people think.
The Recommended Dietary Allowance (RDA) for protein is 0.36 grams per pound of body weight per day (0.8 g/kg). For a 180-pound person, that's approximately 65 grams of protein per day. This is the amount research indicates is sufficient to maintain muscle mass for most adults. Many people in developed countries already exceed this amount through their normal diet without trying.
The fitness industry has popularized the idea that you need 1 gram per pound of body weight or more. However, eating more protein beyond the minimum required amount does not add muscle. What adds muscle is progressive overload -- challenging your muscles with increasing resistance over time. Your body needs adequate protein to support the muscle-building process, but shoveling down extra protein shakes on top of an already sufficient diet does not accelerate muscle growth. The stimulus for growth comes from training, not from excess protein.
Sugar
Sugar is a carbohydrate. That's it. Chemically, it is a simple carbohydrate that your body uses for energy, just like all other carbohydrates.
Some people may choose to regulate their sugar intake as part of a weight loss strategy -- reducing sugar-dense foods like sodas, candy, and desserts can be an effective way to reduce overall caloric intake since these foods are calorie-dense and not very satiating. Others may limit sugar intake at the advice of a doctor, particularly if managing conditions like type 2 diabetes or insulin resistance.
However, sugar itself -- and carbohydrates more broadly -- should not be demonized. Carbohydrates are your body's preferred energy source, they fuel your workouts, and they can absolutely be a component of a healthy diet. The dose makes the poison. A diet that includes moderate amounts of sugar within an overall balanced caloric intake is perfectly compatible with a healthy body fat percentage and good health outcomes. The goal is not to eliminate any single food group -- it's to maintain a sustainable eating pattern that supports your health metrics over the long term.
References
- Jayedi A, Khan TA, Aune D, Emadi A, Shab-Bidar S. Body fat and risk of all-cause mortality: a systematic review and dose-response meta-analysis of prospective cohort studies. Int J Obes. 2022;46(9):1573-1581.
- Annals of Family Medicine. Body Mass Index vs Body Fat Percentage as a Predictor of Mortality in Adults Aged 20-49 Years. Ann Fam Med. 2025;23(4):337.
- Neeland IJ, Ross R, Despres JP, et al. Visceral and ectopic fat, atherosclerosis, and cardiometabolic disease: a position statement. Lancet Diabetes Endocrinol. 2019;7(9):715-725.
- Kim TN, Park MS, Kim YJ, et al. Association of muscle mass and fat mass with insulin resistance and the prevalence of metabolic syndrome in Korean adults: a cross-sectional study. Sci Rep. 2018;8(1):2703.