Swimming to lose weight: what the studies show, and how to train in the pool

Why water suits a heavier body

On land, every step loads the knees, hips and ankles. In water, buoyancy supports part of the body weight. The CDC sums up the practical effect: people are able to exercise longer in water without increased joint or muscle pain, and water-based exercise offers benefits for people with chronic conditions such as diabetes, heart disease and arthritis.

For someone living with obesity, joint pain or back trouble, this can be the difference between an activity that lasts a fortnight and one that lasts a year. Our guide to exercise for obesity puts swimming alongside walking and cycling as the gentlest starting points.

What the studies show on weight

The Cox trial is one of the few to compare swimming directly with another activity over a long period. Sedentary women aged 50 to 70 swam or walked three times a week at a moderate intensity, supervised for six months, then on their own for six months.

• After six months, waist and hip circumferences were lower in the swimmers, and their insulin response to a glucose test was better.
• After twelve months, swimming had reduced body weight by 1.1 kg relative to walking, and total and LDL cholesterol were lower.
• Fitness improved in both groups and was maintained at a year.

The authors concluded that the type of exercise can influence the health benefits. The study involved older women only, so the results cannot be applied to everyone. But they contradict the popular claim that swimming does not help with weight.

How hard to swim

The CDC places recreational swimming in the moderate category and swimming laps in the vigorous one. Water aerobics classes count as moderate.

Measuring effort in the water is less easy than on land. Three practical methods:

• Breathing: at a moderate pace you could say a short sentence at the wall without gasping; at a vigorous pace you could only say a few words.
• Pulse at the wall: count for 15 seconds right after a length and multiply by four, then compare with the zones from the calculator on this page.
• Perceived effort: on a scale of 0 to 10, moderate is about 5 or 6, vigorous 7 or 8.

The calculator estimates your maximum heart rate from your age and your zone 2 range from your resting pulse. Our guide to zone 2 heart rate explains why steady moderate work is a good base.

If you are not a strong swimmer

Many adults avoid the pool because their technique is weak. There are several ways in:

• Water walking and aqua jogging in the shallow end, or in deep water with a float belt.
• Water aerobics classes, which the CDC lists as moderate activity.
• Kickboard lengths, which work the legs and build stamina while you learn to breathe.
• Adult swimming lessons, which pay off quickly: a smoother stroke lets you swim longer.

Any of these counts towards the 150 to 300 minutes of moderate activity a week recommended by the WHO.

A twelve-week plan

This plan is an example to adapt to your level:

1. Weeks 1 to 4: two or three sessions of 20 to 30 minutes, alternating one length of swimming or kicking with a short rest at the wall.
2. Weeks 5 to 8: three sessions of 30 to 40 minutes, with blocks of four to six lengths at a steady pace.
3. Weeks 9 to 12: three or four sessions of 40 to 45 minutes, including one with intervals: for example eight fast lengths with 30 seconds of rest between each.

For weight, the American College of Sports Medicine figures are a useful compass: 150 to 250 minutes a week of moderate activity give a modest loss on their own, more than 250 minutes are linked to clinically significant loss, and a moderate change in eating amplifies the effect.

Mistakes that slow progress

• Swimming slowly with long breaks. Pleasant, but closer to light activity. Keep rests short once your technique allows it.
• Eating more after the pool. Many people feel hungry after swimming; plan a sensible snack rather than improvising. Our guide to calorie needs helps.
• Skipping strength work. Two short strength sessions a week help preserve muscle while you lose fat.
• Judging by the scales alone. Measure your waist too; in the Cox trial, it changed before the weight did.

To compare swimming with other options, see the best sports for weight loss.

If you have a heart condition, high blood pressure, epilepsy, breathing problems or a high body weight, or have not exercised for a long time, talk to your doctor before you start. Never swim alone if you have a condition that could cause a loss of consciousness, and stop if you feel chest pain or unusual breathlessness.

Keep the habit with Never Skip Club

Pool sessions slip easily when the week gets busy. Create your free account on Never Skip Club and add guided strength sessions of 20 or 30 minutes on non-pool days, at home or in a hotel room. Start a crew with friends and a shared weekly rhythm: the ranking rewards regularity, sessions done against sessions planned, so steady swimmers do as well as fast ones. If you want an expert to shape your plan, find a coach from our network, or sign in to your account.