NEAT and Daily Energy Expenditure in Midlife

The Forgotten Component of Energy Expenditure

Non-exercise activity thermogenesis (NEAT) refers to the energy expended during daily living activities: occupational tasks, household chores, shopping, fidgeting, changes in posture, and spontaneous movement unrelated to formal exercise. NEAT is distinct from both basal metabolic rate (the energy cost of maintaining basic physiological functions at rest) and exercise-induced thermogenesis (energy expended during structured physical activity).

NEAT often accounts for 15–30% of total daily energy expenditure (TDEE) in adults, making it a substantial contributor to energy balance. For a sedentary office worker, NEAT might represent 15–20% of TDEE, while for an active occupation (nurse, retail worker, construction), NEAT might exceed 30% of TDEE.

Observational Patterns in Midlife

Research and observational data suggest that NEAT declines during midlife, particularly in women transitioning through perimenopause and into post-menopause. Several life stage factors contribute:

• Career stabilisation: By age 50, many women have reached stable positions in their careers. Occupational tasks may become more standardised, with reduced variability in movement patterns compared to earlier career stages with greater role transitions and mobility.
• Occupational transitions: Some women shift toward less physically demanding roles or sedentary work (management, administration) by midlife. This reduces occupational NEAT relative to younger years.
• Recreational activity shifts: Leisure pursuits may change—shift from high-movement activities (sports, dancing) to lower-movement alternatives (reading, hobbies) reflecting age, interests, or joint health considerations.
• Reduced fidgeting and spontaneous movement: Observational evidence suggests that fidgeting, postural changes, and spontaneous movement decrease modestly with age. This "restlessness" decline may reflect neuromotor or motivational changes.
• Increased sedentary time: Time spent sitting (working, commuting, leisure screen time) increases for many women in midlife, directly reducing NEAT-associated movement.
• Physical discomfort or limitations: Joint pain, musculoskeletal issues, or other age-related physical challenges may reduce voluntary movement, lowering NEAT.
• Hormonal influences: Some research suggests that declining oestrogen and activity-motivation neural systems may modestly reduce spontaneous activity drive, though this is less well-established than other mechanisms.

Magnitude of NEAT Decline

Cross-sectional studies comparing NEAT between age groups suggest average declines of 200–400 kcal/day when comparing sedentary 50+ year olds to their 20–30 year old counterparts. For a woman transitioning from age 40 to age 60, estimated NEAT declines range from 100–250 kcal/day depending on lifestyle changes and activity patterns.

This is a meaningful contributor to total daily energy expenditure. A decline of 150 kcal/day from reduced NEAT, combined with 200 kcal/day from reduced REE (due to muscle loss), totals 350 kcal/day reduction in TDEE. Over a year, this represents approximately 128,000 kcal difference—equivalent to approximately 18 kg of body weight change if energy intake remains constant. This magnitude explains why many women observe gradual weight gain through midlife without increases in food intake.

Individual Variability

NEAT decline in midlife is not universal or inevitable. Women who maintain active occupations, pursue physically engaging hobbies, and consciously maintain spontaneous movement show substantially smaller NEAT declines. Some research suggests that individuals with naturally higher fidgeting propensities may sustain higher NEAT into later life through behavioural consistency.

Critically, NEAT is substantially modifiable. Unlike resting metabolic rate, which is difficult to alter significantly, NEAT can be increased through intentional lifestyle choices: taking stairs, parking further away, standing during phone calls, regular walking, and occupational choice. This makes NEAT a potentially actionable component of energy balance in midlife.

Interaction with Other Metabolic Changes

NEAT decline in midlife occurs alongside other metabolic shifts (reduced REE from sarcopenia, altered insulin sensitivity, fat redistribution). These changes operate synergistically, creating a larger total shift in energy balance than any single factor would explain. Understanding NEAT as one component—modifiable and behavioural—within a broader metabolic context provides nuance to midlife metabolic changes.

NEAT and Energy Balance

From an energy balance perspective, NEAT reduction is equivalent to reduced total daily energy expenditure without changes in intake. The body does not distinguish between whether energy expenditure declines from reduced exercise, reduced NEAT, or reduced REE—the energy balance equation remains the same. A woman whose total daily expenditure declines 250 kcal/day due to NEAT changes experiences the same energy balance shift as if her REE had declined 250 kcal/day.

Understanding this context is important: energy balance shifts in midlife reflect both metabolic (REE) and behavioural (NEAT, exercise) changes. Addressing NEAT through activity modification is an evidence-supported approach to maintaining energy balance, distinct from and complementary to addressing the hormonal and compositional drivers of reduced REE.