You don't have to bust a gut to reap significant benefits from regular, moderate exercise. The science shows real improvements to be found in many areas of your health, independent of weight loss.
In a large European study of 334,161 men and women, the risk of all-cause mortality (death) was reduced by 16-30% for individuals who moved from being classed as "inactive" to being "moderately inactive". This effect was seen across all categories of BMI (Body Mass Index) and waist circumference measurements in the study, suggesting even a small increase in activity levels can have health benefits, even if the increased activity did not result in any weight loss for individuals classed as overweight or obese.
"The greatest reductions in all-cause mortality risk were observed between the inactive and the moderately inactive groups across levels of general and abdominal adiposity, which suggests that efforts to encourage even small increases in activity in inactive individuals may be of public health benefit".
Ekelund, et. al. (2015).
In a small study of 37 participants, regular physical activity was shown to improve endothelial function (the function of the linings of the blood vessels), a risk factor in the development of cardiovascular disease. These improvements were seen even in the absence of weight loss, or any improvements in body fat percentage or blood pressure.
Regular physical activity has also been shown to improve the body's sensitivity to insulin. Insulin resistance (poor sensitivity to insulin) can progress to Type 2 diabetes if unchecked. A combination of 30 minutes of moderate activity, 3-5 days a week, along with a few dietary modifications, can have an even greater effect.
Physical activity throughout your life can even impact the length of telomeres - a measurement of ageing at the cellular level. A study of 69 men and women aged 50-70 showed that regular moderate activity resulted in longer telomeres than less active individuals. Interestingly, individuals that engaged in far higher levels of physical activity showed similar telomere lengths to the inactive participants, suggesting there may be a "sweet spot" in the middle ground.
Physical activity may even reduce the risk of the formation of gallstones! A study of 25,639 40-74 year-olds demonstrated there was a 70% reduction in the risk of developing symptomatic gallstones amongst the most active study participants.
As for the benefits to mental health - research has shown reductions in stress and anxiety levels, and improvements in mood, from regular activity. Exercising regularly can also improve the quality of your sleep, and if you exercise outside, you'll boost your vitamin D levels too.
It's important to choose activities you enjoy, and start with what you can reasonably fit around your current commitments. If you miss a day or two when life gets busy, don't beat yourself up over it - tomorrow is another day. Always check with your General Practitioner before starting a new exercise if you have been inactive, in case there are any health issues that could impact your safety or wellbeing.
References:
Banim, P.J., Luben, R.N., Wareham, N.J., Sharp, S.J., Khaw, K.T., & Hart, A.R. (2010). Physical activity reduces the risk of symptomatic gallstones: A prospective cohort study. European Journal of Gastroenterology and Hepatology, 22(8), 983-988.
Bird, S.R., & Hawley, J.A. (2017). Update on the effects of physical activity on insulin sensitivity in humans. BMJ Open Sport and Exercise Medicine. doi: 10.1136/bmjsem-2016-000143
Dow, C.A., Stauffer, B.L., Brunjes, D.L., Greiner, J.J., & De Souza, C.A. (2017). Regular aerobic exercise reduces endothelin-1-mediated vasoconstrictor tone in overweight and obese adults. Experimental Physiology, 102(9), 1133-1142.
Ludlow, A.T., Zimmerman, J.B., Witkowski, S., Hearn, J.W., Hatfield, B.D., & Roth, S.M. (2008). Relationship between physical activity level, telomere length, and telomerase activity. Medicine and Science in Sports and Exercise, 40(10), 1764-1771.
Ekelund, U., et. al. (2015). Physical activity and all-cause mortality across levels of overall and abdominal adiposity in European men and women: The European Prospective Investigation into Cancer and Nutrition Study (EPIC). American Journal of Clinical Nutrition, 101, 613-621.
Mental Health Foundation of New Zealand. (n.d.). Physical activity for mental wellbeing. [PDF]. Retrieved September 21, 2018, from https://www.health.govt.nz/system/files/documents/topic_sheets/physical-activity-mental-wellbeing-english_0.pdf