Browse the evidence

Stand-alone use of commercially available smartphone fitness apps (immersive or non-immersive) does not significantly improve cardiorespiratory fitness or physical activity levels in insufficiently active adolescents compared to usual behavior.

Downloading a fitness app is not a workout. If you want to improve your fitness, you must use the app consistently (ideally 3x/week) and push yourself to the required intensity. Simply having the app installed and using it occasionally will not change your cardiorespiratory fitness.

High-frequency spicy food consumption is inversely associated with mortality from specific causes: cancer, ischemic heart disease, and respiratory diseases.

Eating spicy foods frequently may help protect against death from cancer, heart disease, and respiratory issues. This benefit is part of the overall mortality reduction seen with high spicy food intake.

Oleic acid stimulates complete fatty acid oxidation in skeletal muscle by activating the cAMP/PKA pathway, which phosphorylates and activates SIRT1, leading to PGC1α deacetylation and increased expression of fatty acid oxidation genes.

Consuming oleic acid (found in olive oil and other monounsaturated fats) may actively signal your muscles to burn fat more efficiently by activating specific cellular pathways (SIRT1/PGC1α). This is distinct from saturated fats, which do not trigger this specific oxidation-promoting signal. Prioritizing monounsaturated fats may support metabolic flexibility.

Oral estrogen therapy in postmenopausal women causes adverse body composition changes (increased fat mass, decreased lean body mass) compared to transdermal estrogen, mediated by a first-pass hepatic suppression of lipid oxidation and IGF-I levels.

If you are using estrogen replacement therapy, the method of delivery matters for your body shape. Oral estrogen (pills) can lead to increased body fat and loss of muscle mass in postmenopausal women, likely due to how the liver processes the hormone. Transdermal estrogen (patches) avoids these specific metabolic shifts. Discuss route-specific metabolic impacts with your provider if body composition is a concern.

The protective effect of physical activity against dementia is conditional on APOE ε4 genotype, being significant only in non-carriers, and is attenuated or non-significant in long-term follow-up (22 years).

If you carry the APOE ε4 gene, physical activity may not protect your brain from dementia as effectively as it does for others. However, for those without this genetic risk factor, maintaining physical activity is a strong protective strategy against dementia, especially after age 75.

Reduced insulin/IGF-1 signaling (IIS) extends lifespan across species by conserving specific biological processes—specifically, the down-regulation of protein biosynthesis and the up-regulation of cellular detoxification (including GSTs)—rather than by conserving specific orthologous genes.

Focus on maintaining healthy insulin sensitivity and cellular detoxification pathways rather than searching for a single 'magic bullet' gene. Interventions that reduce insulin signaling (like caloric restriction or specific pharmacological agents) may promote longevity by triggering these conserved process-level responses (reduced protein synthesis, increased detoxification) rather than by acting on a single specific gene target.

Bariatric surgery-induced weight loss in morbidly obese patients significantly improves insulin sensitivity, endothelial function, and specific inflammatory markers (CRP, sialic acid, E-selectin, P-selectin, vWF, PAI-1), although proinflammatory cytokines (TNF-alpha, IL-6) may remain elevated.

For morbidly obese individuals, bariatric surgery can significantly improve insulin sensitivity and endothelial function within months, reducing cardiovascular risk. However, not all inflammatory markers (like TNF-alpha and IL-6) may normalize, suggesting that metabolic stress or residual adiposity might sustain some inflammatory pathways. This highlights the importance of addressing insulin resistance specifically.

Self-administration of polydrug androgenic-anabolic steroid (AAS) regimens for 8-14 weeks significantly decreases HDL-C, HDL2-C, HDL3-C, and Apo-A1, while increasing Apo-B, creating a highly atherogenic lipid profile.

Using multiple anabolic steroids at high doses significantly worsens your cholesterol profile by lowering 'good' cholesterol (HDL) and raising 'bad' markers (Apo-B). This effect is not subtle; it creates a high-risk state for heart disease that does not immediately resolve after you stop using the drugs, especially if you use them for longer periods (14 weeks vs 8 weeks).

In older adults and those with insulin resistance, brain glucose uptake is significantly reduced (hypometabolism) in specific regions (frontal, temporal, parietal cortex), creating an energy deficit that precedes cognitive decline and Alzheimer's Disease.

If you are over 65 or have metabolic risk factors like insulin resistance, your brain may be using less glucose even if your memory seems fine. This 'energy deficit' is a known precursor to cognitive decline. While this paper doesn't prescribe a fix, it highlights that maintaining metabolic health (managing blood sugar/insulin) is critical for brain fuel supply in later life.

Ketone bodies (beta-hydroxybutyrate and acetoacetate) serve as an effective alternative fuel for the brain in aging and Alzheimer's Disease because ketone uptake remains normal even when glucose uptake is impaired.

Your brain can switch to burning ketones for fuel even if you have early Alzheimer's or cognitive decline. This metabolic flexibility exists, which is why strategies that raise ketone levels (like ketogenic diets or MCT oil) are being explored to support brain function in aging.

Disruption of the skeletal muscle molecular clock (specifically Bmal1 loss) causes severe muscle pathology, including reduced force production, altered sarcomeric structure, and impaired mitochondrial respiration.

Maintain consistent sleep and feeding schedules to keep your muscle clocks synchronized. Disrupted rhythms (like shift work or erratic eating) may impair muscle strength and mitochondrial health, even if you exercise. Prioritize regularity in daily habits to support muscle maintenance.

Time-restricted feeding and scheduled physical activity can entrain the skeletal muscle molecular clock, shifting gene expression phases to align with metabolic demands.

Try to align your main meals and workouts with your active hours. For example, eating earlier in the day or exercising before your main meal may help synchronize your muscle clocks. Consistency in timing is key to maintaining metabolic health.

Inhibition of the Insulin/IGF-1 Signaling (IIS) pathway extends lifespan in multiple species by enhancing mitochondrial function, biogenesis, and mitophagy.

Genetic variants that naturally result in lower IGF-1 levels are associated with human longevity. While not a direct prescription, this suggests that the hormonal environment of reduced growth signaling may be protective against aging, distinct from the muscle-building goals of high IGF-1 in youth.

Activation of AMPK by dietary restriction or compounds like metformin extends lifespan by inhibiting mTOR and promoting mitochondrial biogenesis.

Dietary restriction activates AMPK, which improves mitochondrial health and extends lifespan. If strict dieting is not feasible, compounds like metformin (which activate AMPK) or time-restricted eating may offer similar metabolic benefits.

Insulin regulates free fatty acid (FFA) appearance in plasma primarily by inhibiting lipolysis, while maintaining a constant absolute rate of primary intra-adipocyte FFA reesterification.

Insulin controls blood fat levels mostly by stopping fat cells from releasing fat, not by burning it. This happens at relatively low insulin levels. High insulin levels are needed to significantly change how much fat your muscles burn. For weight management, keeping insulin levels stable helps prevent fat release from adipose tissue.

Improvements in maximal oxygen uptake (VO2max) following aerobic training are not correlated with improvements in aerobic performance (time trial capacity) in previously sedentary individuals.

If you are training to improve your endurance performance (like running or cycling time trials), do not rely solely on increasing your VO2max. Instead, focus on training that improves your metabolic efficiency at submaximal intensities. This includes managing lactate accumulation and improving the economy of movement. Standardizing training intensity as a fixed percentage of VO2max may not be the most effective way to improve performance because it does not account for individual metabolic responses.

Metformin is not recommended for treating NAFLD or NASH in humans despite improving insulin sensitivity in animal models.

Do not rely on metformin to treat your fatty liver. While it helps control blood sugar in diabetes, studies show it does not improve liver health in people with NAFLD or NASH. Focus on weight loss and dietary changes instead.

Gut microbiota depletion via broad-spectrum antibiotics significantly reduces skeletal muscle endurance and fatigue resistance in healthy mice, an effect mediated by altered glucose homeostasis and muscle glycogen levels rather than changes in muscle mass or mitochondrial function.

Maintaining a healthy gut microbiome is important for muscle endurance. While this study used mice, it suggests that factors disrupting gut bacteria (like broad-spectrum antibiotics) may temporarily reduce your stamina and fatigue resistance. Restoring gut health (natural reseeding) can reverse these effects. Focus on fiber-rich foods and fermented foods to support gut bacteria, which may help optimize glucose availability for your muscles during exercise.

Genetic inactivation of brain fatty acid synthase (FAS) in the hypothalamus causes hypophagia and increased physical activity by impairing PPARα signaling, which can be reversed by administering a PPARα agonist.

This research identifies a specific brain mechanism where the enzyme FAS helps regulate appetite and activity by activating PPARα. While this doesn't suggest a direct supplement or drug for humans yet, it highlights that brain metabolism of fats plays a crucial role in energy balance, distinct from peripheral fat storage.

Reduced insulin/insulin-like growth factor (IIS) signaling extends lifespan and healthspan in model organisms but is associated with reduced skeletal muscle mass and function in aging humans.

Genetic studies show that dampening IGF-1 signaling can extend lifespan in mice, even if it reduces muscle size. However, in humans, low IGF-1 is linked to sarcopenia and frailty. The key takeaway is not to suppress IGF-1 artificially, but to understand that the pathways driving muscle growth (like mTOR) are the same ones that, when chronically overactive, might accelerate aging. The goal is balance: maintaining muscle through exercise and adequate protein without necessarily maximizing anabolic signaling to the point of potential cellular stress.

Dietary restriction (DR) extends lifespan and healthspan in model organisms, but its impact on skeletal muscle mass is complex, potentially attenuating age-related loss in some species while causing absolute mass decrease in others.

Dietary restriction is the most reliable way to extend lifespan in animals. In rats and monkeys, it also helps preserve muscle mass by reducing inflammation and oxidative stress. For humans, this suggests that moderate caloric restriction, combined with resistance training and adequate protein, might help maintain muscle function and healthspan, even if it doesn't maximize muscle size. The focus should be on nutrient density and metabolic health rather than just caloric deficit.

Higher birth weight is positively related to subsequent grip strength across the lifespan, suggesting early biological imprints on muscle capacity.

Your birth weight may have set a baseline for your muscle strength potential. While you cannot change your birth weight, this highlights the importance of early life health and nutrition in building physical reserve.

Plasma LEAP2 levels increase with higher body mass, obesity, and postprandial states in humans and mice, acting as an endogenous antagonist to acyl-ghrelin to limit food intake and blood glucose elevation.

Your body produces a hormone called LEAP2 that increases when you are overweight or after you eat. This hormone acts as a brake on the 'hunger hormone' (ghrelin) to prevent you from overeating and spiking blood sugar. This is a natural regulatory mechanism. While high LEAP2 is associated with obesity, it also decreases when you lose weight, suggesting your body's hormonal 'brakes' can adjust as your metabolic state changes.

Weight loss induces adipocyte shrinkage and metabolic adaptations that create a persistent biological drive to regain weight by increasing nutrient clearance efficiency and lowering energy expenditure, creating an 'energy gap' that promotes overeating.

Understand that after losing weight, your body biologically fights to regain it by making you hungrier and burning fewer calories. This is not a failure of willpower. Successful long-term maintenance requires acknowledging this persistent biological pressure and likely needs comprehensive, persistent strategies (behavioral, environmental, or pharmaceutical) to counter it, rather than relying on willpower alone.