Swimming Nutrition and Supplements: Fuel, RED-S and What Works

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Every swim parent knows the after-practice hunger: a teenager who gets in the car and eats two sandwiches before the parking lot. It isn’t a myth. In one classic study, elite female swimmers in a heavy training block burned about 5,600 calories a day, but ate only about 3,100. Swimming nutrition is mostly about keeping up: eating enough, often enough, around early practices and long meets. This page covers what swimmers need day to day, why female swimmers in particular should know about RED-S (Relative Energy Deficiency in Sport), and which supplements have evidence behind them, with third-party tested picks. It’s general information from the major sports-nutrition bodies, not personal advice.

Prices change often. The prices below are what we saw at the maker or a major retailer in October 2026; check the current price before you buy. Back to the swimming hub.

Why swimmers need so much energy

In that 1997 study, five elite female swimmers training about 17.5 km a day in two sessions spent roughly three times their resting energy. Their food intake fell about 43% short of what they burned. Most swimmers don’t train like that, but the pattern is common: big training loads, early practices that squeeze out breakfast, and appetite that doesn’t always keep up. In a 2023 study of NCAA Division III swimmers in preseason, 43% of the men and women had low energy availability, meaning too little energy left over for the body’s basic needs after training.

Daily eating: match the fuel to the training

A 2014 expert review, “Nutrition for Swimming”, published in the International Journal of Sport Nutrition and Exercise Metabolism, sets out the basics:

• Carbohydrate, 3–10 g per kilogram of body weight a day, moving up and down with training. Heavy doubles sit near the top; easy days and taper sit lower.
• Protein, about 0.3 g per kilogram of high-quality protein right after key sessions and at regular times through the day. Most swimmers can get this from food: eggs, dairy, meat, fish, beans or tofu at every meal and snack.
• Vitamins and minerals from food. A varied diet covers most swimmers’ needs.
• No crash diets. The paper encourages swimmers to avoid rapid weight swings, to change body composition slowly with small food changes if at all, and to match intake to needs during taper, injury and the off-season.
• Young swimmers: the authors urge adolescent swimmers to eat a well-planned diet that covers growth as well as training.

For 5 a.m. practice, that often means something small before (a banana, toast, a glass of milk), then a real breakfast after, a packed lunch, an after-school snack before afternoon practice, and dinner. Meet-day eating is on our Meet Day page, and refueling between doubles on swimmer recovery.

Female swimmers and RED-S

RED-S (the IOC now writes it “REDs”) is what happens when an athlete doesn’t eat enough for the training they do, for long enough or badly enough to cause harm. The International Olympic Committee’s 2023 consensus statement describes it as a syndrome in both female and male athletes that can reduce energy metabolism, reproductive function, bone health, immunity, the body’s ability to store fuel in muscle, and heart and blood health, which together can raise injury risk and hurt performance. Studies have found signs of low energy availability in 23–80% of female athletes and 15–70% of male athletes, depending on the sport and how it was measured.

Swimming has its own evidence. In a study of junior elite female swimmers aged 15–17 over a 12-week season, those whose menstrual hormones were suppressed by low energy got about 10% slower in a 400 m swim, while swimmers with normal cycles improved by about 8%. The IOC statement cites it as an example of how under-fueling hurts training.

Warning signs to take seriously, from the IOC statement:

• Periods that stop, become irregular, or never start (no period by age 15). Missing periods is not a normal side effect of hard training.
• Bone stress injuries (stress fractures) or low bone density.
• Getting sick often, constant tiredness, poor sleep, or training that stops paying off.
• Mood changes, anxiety about food, body dissatisfaction, or exercising extra to “make up” for eating.
• In male swimmers: low libido and other signs of low testosterone.

The IOC also recommends that body composition (skinfolds, body-fat testing) be assessed in athletes under 18 only for medical reasons, because of the pressure it can create. The first treatment is eating enough again, guided by a team that can include a sports medicine doctor, a sports dietitian and a psychologist. If any of these signs sound familiar, talk to a doctor, ideally one who works with athletes. Coaches and parents: comments about weight and “looking fast in a suit” can do real damage. Focus on fueling for performance.

Supplements for swimmers: what the evidence says

The 2014 swimming review says specific supplements may help in some situations, but should be tried only with the support of trained professionals. The IOC’s 2018 consensus statement on supplements reaches the same “food first” conclusion. Here’s how the common ones stack up:

• Sports drinks and electrolytes: sports foods. Useful on long, warm sessions and meet days, when a meal isn’t practical.
• Protein powder: a convenience. Handy right after early practice when there’s no time for food. Not essential if you eat well.
• Creatine and caffeine: some of the stronger evidence, for adults. Expert groups place both among the better-studied performance supplements. Creatine can add body weight. Caffeine isn’t for everyone: side effects include anxiety, upset stomach, poor sleep and a racing heart, which matters with early practices. Neither is for teens (see below). Stay within the label.
• Iron and vitamin D: test, don’t guess. Low iron is more common in female athletes, and the IOC statement links under-fueling with poorer iron status. Indoor swimmers may see little sun in winter. But extra iron you don’t need can do harm, so get a blood test through your doctor first.
• Young swimmers: the American Academy of Pediatrics says caffeinated energy drinks have no place in children’s and teens’ diets and advises against creatine for young athletes. For a teen swimmer the “supplements” that matter are a packed breakfast, a water bottle and snacks in the bag.

Third-party testing: why it matters for swimmers

Swimmers from national level up can be drug-tested in and out of competition, and under anti-doping “strict liability” rules a contaminated supplement is no excuse. One international study found about 15% of 634 supplements contained undeclared prohormones. Programs like NSF Certified for Sport and Informed Sport test products for banned substances. They lower the risk without removing it, and they don’t test whether a product works. If you could ever be tested, use certified products only and check the batch yourself.

Our top picks

Product	In one serving	Certification	About (Oct 2026)	Per serving
Skratch Labs Hydration	400 mg sodium, 19 g carbs	Maker says NSF Certified for Sport (not found in NSF’s database in Oct 2026)	$24 / 20 servings	about $1.20
Nuun Sport	300 mg sodium, 150 mg potassium, 1 g sugar	Informed Choice	$7.49 / 10 tablets	about $0.75
Thorne Whey Protein Isolate	21 g protein	NSF Certified for Sport	$65 / 30 scoops	about $2.17
Thorne Creatine	5 g creatine monohydrate	NSF Certified for Sport	$44 / 90 scoops	about $0.49
Klean Multivitamin	2 tablets; 1,000 IU vitamin D	NSF Certified for Sport	about $46 / 30 servings	about $1.53

Why these five: the three Thorne and Klean products are NSF Certified for Sport, Nuun says its Sport tablets are Informed Choice certified, and Skratch’s maker says it is NSF Certified for Sport (we couldn’t find it in NSF’s search, so look it up before relying on it). Together they cover what swimmers actually use. Skratch Labs Hydration adds carbohydrate to the electrolytes, so it doubles as fuel on doubles and meet days. Nuun Sport is the cheap, low-sugar tablet for the swim bag. Thorne Whey is a simple 21 g protein shake for after early practice. Thorne Creatine is plain creatine monohydrate, for adult swimmers only. The Klean Multivitamin is a basic multi for swimmers with limited diets; it lists no iron, which is a plus if you haven’t been tested. Follow the label for how much to take. Full comparisons: best electrolyte powders, best protein powder for athletes, best creatine and best multivitamin for athletes.

Check the Thorne Whey Protein Isolate price on Amazon

Talk to a professional. Before starting any supplement, check with your doctor or a registered sports dietitian, especially for swimmers under 18 and for anyone who is pregnant, takes medication or has a heart, kidney or other medical condition. This page is general information, not medical advice.

Keep going with swimming training, swimming injuries, or see how team-sport athletes eat on our soccer nutrition page.

Swimming nutrition questions

How many calories does a swimmer need?

It depends on size, age and training. Elite women in a heavy block burned about 5,600 calories a day in one study, while many recreational swimmers need far less. The key is eating enough for your training; ongoing tiredness, missed periods or getting slower can be signs you’re not.

What should swimmers eat before morning practice?

Something small and easy to digest, like a banana, toast or a glass of milk, then a proper breakfast with carbohydrate and protein after practice. A 2014 swimming nutrition review suggests about 0.3 g of protein per kilogram after key sessions.

What is RED-S in swimmers?

Relative Energy Deficiency in Sport: health and performance problems caused by not eating enough for your training. The IOC says it affects female and male athletes and can harm periods, bones, immunity and performance. In one study, under-fueled junior female swimmers got about 10% slower over a season.

Is it normal for a swimmer to lose her period?

No. Missing or irregular periods are a key warning sign of low energy availability in the IOC’s REDs statement. See a doctor, ideally one who works with athletes.

Can teen swimmers take creatine or pre-workout?

The American Academy of Pediatrics advises against creatine for young athletes and says caffeinated energy drinks have no place in teens’ diets. For teen swimmers, enough food is the focus.

Why should swimmers use NSF Certified for Sport products?

Because supplements can contain banned substances not listed on the label, and swimmers who can be drug-tested are responsible for anything in their system. Certified products are tested for banned substances, which lowers the risk.