However, bad habits will be wreaking damage on the inside. Too much dietary fat, sugar and alcohol, as well as too few vitamins, minerals and essential fatty acids, can contribute to the furring of the arteries, reduced insulin sensitivity and fatty deposits around internal organs.
But the most important health decision you can make now is not to smoke, as it will become increasingly difficult to give up as you get older.
How can I maintain my health in my 20s?
If your activity level involves walking to the bar or ripping the packaging off a ready meal, it's time to wake up to reality.
Heart disease is one of the biggest killers of men, and a poor diet and insufficient physical activity are the prime causes.
If you've had a break from exercise, ease yourself back in slowly, allowing a period of weeks (not days) to increase the volume of activity.
Always warm up before you step up the pace, and consider adding strength training to your regime to make muscles and connective tissues more robust. Make stretching part of your routine, and don't ignore aches and pains. It's more sensible to take a few days off - and if the problem doesn't go away, see a sports medicine professional.
Vices such as smoking and drinking excessively can deplete your body of vitamins and minerals. Heavy drinking and smoking increase the need for the B vitamins and vitamin C, and may affect zinc absorption. These needs can be satisfied by eating meat, shellfish, dairy products and whole grains.
Drinking also increases the need for folate (found in yeast extract, beans and pulses, breakfast cereals, liver and wheatgerm) and magnesium (in whole grains, nuts and seeds).
Smokers may want to up their intake of vitamin E (in vegetable oils, avocados, nuts and seeds), as well as stock up on watercress and broccoli, which are high in phenethyl isothiocyanate - a phytochemical shown to reduce the risk of tobacco-induced lung cancer.
LIFE IN YOUR 30s
According to the Harvard Medical School, you're likely to lose 5 to 15 per cent of your aerobic capacity for each decade after the age of 30. So the rot starts here. But, as experts point out, exercise regularly and you can combat this natural decline.
What's more, being physically fit can dramatically reduce men's deaths from heart disease, even when cholesterol rates are high, according to research from Queen's University in the United States.
Doing the equivalent of four to five 30-minute workouts A week was found to be sufficient to significantly reduce the risk of heart disease.
How can I maintain my health in my 30s?
It's all too easy to slip into an exercise comfort zone - but be prepared to step outside of it regularly. If you want to stay quick, Harvard Medical School recommends adding speed work to aerobic workouts. Using weights, two to three days a week, combats the natural loss of muscle mass as you age, too.
A recent study in Sports Medicine also found weight training helps stimulate the release of growth hormone, which regulates body-fat storage - thereby keeping your beer belly at bay.
LIFE IN YOUR 40s
With your career reaching its peak, your free time limited, your kids growing up and your earning requirements spiralling, stress often reigns in this decade. However, research proves exercise can give you more energy, help you become more "stress-resistant", and allow you to burn off anxiety.
But many men are stuck in a catch-22 situation, where they don't feel they have the time and energy to devote to workouts.
However, even if you can't find hours to spend at the gym, incorporating more activity into your lifestyle will help. Stop driving to work if you can walk or cycle; stop working through your lunch break; and ensure that some of your family time is spent doing active things, rather than slumping in front of the TV.
How can I maintain my health in my 40s?
Now is the time to take control of the stress factors in your life. If you don't even have time to walk for 30 minutes on five days of the week, you have to assess your work-life balance.
And calorie-blasting doesn't have to take place at the gym. Playing sports in the park, dog walking, or going on a family bike ride or hike will all help you burn more calories.
Research from the University of Arkansas reveals the amount of energy spent on daily activity accounts for 75 per cent of the variability in body-fat levels - so the more active you are, the less body fat you'll have.
The other thing to think about is flexibility. Muscles lose elasticity and the connective tissues around our joints thicken as we get older, leading to a reduced range of motion and a greater risk of stiffness, aches and pains. Stretching, rotating, bending and extending your joints regularly - along with activities such as tai chi, yoga and Pilates - can help to restore a good range of motion.
LIFE IN YOUR 50s
According to Australian Government statistics, men in their 50s are in the healthiest state they've been for decades.
Perhaps with less need to "prove themselves" in the workplace and with children growing up, middle-aged men are able to spend a bit more time on themselves.
At the VA Medical Centre in Salt Lake City, Utah, physically fit men in their mid 50s were were in better shape than inactive men in their mid 20s. Amazingly, active older men had lower resting heart rates than younger men - 64 beats per minute versus 85 beats per minute for the younger men - as well as higher oxygen uptake during maximal exercise, and a better recovery heart rate one minute after exercise than men in their 20s.
So it isn't too late to reap the benefits. And it's well worth doing: in research from the Journal of Aging and Physical Activity, the risk of walking difficulties was highest among men aged 40 to 64 who engaged in a fitness activity once a week, compared with men who were active three times a week.
How can I maintain my health in my 50s?
As far as your heart health is concerned, cardiovascular exercise is the key. Resistance training is arguably as essential to physical health in your later years as it is earlier in life. It strengthens your muscles and bones, and there are indications it is helpful in lowering cholesterol levels, as well as improving glucose uptake (thereby reducing the risk of diabetes) and strengthening the ligaments and tendons to reduce pressure on your joints.
In the past, people with high blood pressure, heart diseases and conditions such as arthritis were warned to avoid using weights, but researchers at Harvard Medical School have found weight training has no adverse effect on blood pressure or heart function.
So get pumping: you might end up with brains as well as brawn if you do. Two recent studies found vigorous workouts at least twice a week could reduce the risk of developing Alzheimer's by 50 per cent, and Parkinson's by up to 60 per cent.
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