Over time, changes in body fat mass result from the consistent difference between the amount of energy consumed and the amount of energy expended.
Mechanism
Synthesis from 4 studies
Over time, your body fat goes up if you eat more than you burn, and down if you burn more than you eat — this balance is controlled by how much energy your muscles and liver use, and by a hormone called leptin that tells your brain to eat less when fat stores are high, as shown in...
Most probable mechanism
When you consistently burn more calories than you eat, your body breaks down fat for energy, and your muscles and liver get better at using fat as fuel; when you eat more than you burn, your fat cells store more fat, and your body releases a hormone called leptin to tell you to eat less and burn more — this balance, not weight cycling or fat cell shape changes, is what ultimately controls how much fat you have over time, as shown in studies of intense training, weight cycling, and genetic fat cell changes.
Chronic negative energy balance reduces adipose tissue mass by mobilizing stored triglycerides into free fatty acids for oxidation in muscle and liver, driven by increased energy expenditure from exercise and elevated resting metabolic rate, as demonstrated in 10.1371/journal.pone.0202390 and 10.3390/nu9101149.
Increased energy expenditure arises from elevated resting metabolic rate due to gain in fat-free mass from resistance training, enhanced post-exercise oxygen consumption (EPOC), and increased mitochondrial oxidative capacity in skeletal muscle, all of which amplify daily energy burn and sustain negative energy balance, as shown in 10.1371/journal.pone.0202390.
Positive energy balance activates adipocyte YAP/TAZ signaling via reduced LATS1/LATS2 activity, which directly upregulates leptin gene transcription independently of fat mass, increasing circulating leptin to suppress appetite and elevate energy expenditure, as demonstrated in 10.1038/s42255-024-01045-4.
Leptin signaling increases whole-body energy expenditure and shifts substrate utilization toward fatty acid oxidation, primarily in the liver, preventing ectopic lipid accumulation and maintaining metabolic homeostasis during energy surplus, as shown in 10.1038/s42255-024-01045-4.
Repeated cycles of weight loss and regain without net energy imbalance do not increase long-term fat mass, confirming that cumulative energy balance — not weight fluctuation history — determines adipose tissue storage, as shown in 10.3390/nu9101149.
Less supported by current evidence, but not ruled out
Genetic activation of YAP/TAZ in fat cells can shrink them by turning them into less fat-storing cells, but this does not override the need for energy balance to control long-term fat mass, as shown in 10.1038/s42255-024-01045-4.
Deletion of LATS1/LATS2 in adipocytes causes YAP/TAZ to enter the nucleus and suppress PPARG, leading to loss of lipid droplets and conversion of mature fat cells into progenitor-like cells, reducing fat mass without altering energy intake or expenditure, as shown in 10.1038/s42255-024-01045-4.
This fat loss is accompanied by elevated leptin production via YAP/TAZ-driven transcription, which compensates by increasing energy expenditure and preventing metabolic disease, indicating that even when fat cells shrink, energy balance is still regulated through leptin, as shown in 10.1038/s42255-024-01045-4.
Evidence from Studies
Supporting (4)
Community contributions welcome
Limited Sex Differences in Energy Balance and Body Composition during 61+D of US Army Ranger Training
Hippo–YAP/TAZ signalling coordinates adipose plasticity and energy balance by uncoupling leptin expression from fat mass
Contradicting (0)
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Gold Standard Evidence Needed
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