When on patrol, submariners spend several months submerged and isolated.
They work shifts, endure a disrupted pattern of sleep, and eat a restricted diet.
Space for physical activity is limited and there is no exposure to natural sunlight.
Surprisingly, none of these seems to have a deleterious effect on biomarkers of cardiometabolic risk (Gunner et al. 2020).
A study among Royal Navy submariners found that during a voyage there was a tendency to lose weight and for serum lipids levels to improve.
Gunner, F., Lindsay, M., Brown, P., Shaw, A., Davey, T., Lanham-New, S., Griffin, B. & Fallowfield, J. (2020) Impact of the occupational environment of a submerged submarine on cardiometabolic health of Royal Navy submariners. Occupational & Environmental Medicine. 77(6). https://oem.bmj.com/content/77/6/368.