Only high-intensity interval training, not moderate-intensity training, reduced fat mass and preserved lean mass in healthy older adults. Digest
As people age, reducing body fat without accelerating the loss of muscle becomes increasingly difficult. Moderate-intensity exercise is widely prescribed for older adults, yet it may not provide enough stimulus to protect lean tissue during fat loss. In a 6-month randomized trial, researchers compared three exercise intensity prescriptions and tracked body composition with dual-energy X-ray absorptiometry (DXA).
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Adults ages 65–85 completed three supervised 45-minute exercise sessions per week for 6 months. High-intensity interval training (HIIT) used four 4-minute treadmill bouts at 85–95% of peak heart rate with active recovery, while moderate-intensity continuous training (MICT) used steady walking at 60–70%. A low-intensity active control group completed balance, stretching, and toning exercises at 45–55%. DXA measured fat mass, fat-free mass (nonfat tissues, including muscle), body fat percentage, and visceral adipose tissue (fat stored around abdominal organs).
- Both HIIT and MICT lowered fat mass more than the low-intensity control, with no clear difference between the two treadmill programs (about 1 kg lower than control at 6 months).
- MICT was linked to a decline in fat-free mass, while HIIT maintained it.
- Only HIIT produced a clear net reduction in body fat percentage across 6 months.
- Visceral adipose tissue decreased over 6 months in both HIIT and MICT. At month 6, only MICT was clearly lower than control, while HIIT showed a similar direction.
- To judge whether reductions in body fat percentage and visceral fat exceeded normal DXA scan variability, the researchers set conservative cutoffs, and by that standard, average body fat and visceral fat changes were too small to count as clinically meaningful. More people improved with HIIT, but not enough to clearly separate it from the other programs.
Higher-intensity training may provide a stronger stimulus for muscle maintenance through greater mechanical loading and higher rates of muscle protein synthesis. HIIT also imposes a higher energetic and metabolic demand, which enhances fat loss without requiring longer training sessions. These combined effects offer a plausible explanation for why HIIT preserved lean tissue better than MICT.
The findings suggest that HIIT may be preferable to MICT when the goal is to reduce body fat without accelerating lean mass loss. However, the results also highlight the limits of aerobic exercise as a standalone strategy, supporting the need for targeted approaches, such as combining higher-intensity aerobic work with resistance training and dietary support, to meaningfully alter body composition during aging. In this clip, Dr. Brad Schoenfeld describes the importance of resistance training and adequate protein intake to prevent losing muscle mass during weight loss.