Marathon Swimming Nutrition – Index of Articles

I’ve written a variety of posts over the last few years on nutritional considerations in marathon swimming. Here they are in one place for your reference.

Series: The Art & Science of Marathon Swimming Nutrition

On Recovery Drinks – includes a DIY powdered recovery drink recipe

On Maltodextrin – Maxim vs. Carbo Pro

Series: On Nutritional Science in Marathon Swimming

On Peter Attia’s nutrition webinar

Marathon swimming and low-carbohydrate diets

Marathon Swimming Nutrition: Do it yourself

The last in a series of four posts about nutrition in marathon swimming. To recap:

  • Marathon swimming nutrition is both art and science. There are both “best practices” (generalizable to many) and “special sauce” (generalizable to few). In general, a nutrition plan that aims to drink some carbs — not too much is a good place to start.
  • Some carbohydrates are “better” than others, due to differences in osmolality. An endurance athlete can consume more carbohydrate in the form of maltodextrin, compared to simple sugars, without overwhelming the digestive system. Also, maltodextrin is neutral in taste, thus providing more control over your drink’s flavor.
  • Of the many designer endurance fuels on the market, few are ideal for marathon swimming. High electrolyte content makes sense for runners, cyclists, and triathletes – but less sense for swimmers (even less sense for ocean swimmers).

Although I do think Perpetuem is a good product for swimmers, my best advice is to skip the one-size-fits all formulas and do it yourself. This is the only way to ensure you get the nutrition you need on a marathon swim, and not the stuff you don’t need.

There are two basic varieties of “DIY,” the “full DIY” and the “semi DIY.”

The Full DIY

  1. bulk maltodextrinBuy some plain complex carbohydrate – maltodextrin (Carbo-ProMaxim, or bulk) or if you want to be adventurous, Superstarch.
  2. Mix your chosen carb with water, and flavor it with something tasty. Possibilities might include fruit juice or Gatorade.
  3. Calculate your drink recipe by:
    1. how many calories (including the ones in your flavoring) you want to consume per hour
    2. how much fluid you want to consume per hour
  4. If you’ll be swimming in warm water and/or freshwater, add some electrolytes (e.g., Hammer Endurolytes). Keep in mind many fruit juices already provide some potassium.
  5. If you want to add some amino acids, go for it (try this).

This is, in fact, exactly what I do. For a 30-oz feed bottle, I mix:

  • 1/2 cup maltodextrin (bulk for everyday use; Carbo-Pro or Maxim for race day)
  • 6 oz fruit juice – anything but citrus. On my big swims last year I used unfiltered apple juice. But other juices work great too – cranberry (unsweetened), blueberry, cherry, pomegranate, grape, etc. You can even blend them!
  • 24 oz water

This recipe provides approximately 280 calories and 70g carbohydrates (depending on the juice). Assuming bulk maltodextrin ($33.54 per 12 lbs) and premium juice ($4 per quart), the total cost of my 30-oz custom bottle comes to $1.06. For everyday workouts, I dilute the recipe by 50%, bringing my cost down to 53 cents.

Important Caveat: Some people have trouble digesting fructose. Fruit juice contains fructose (along with glucose & some other stuff).

Always test your feed plan before you use it on a marathon swim!

The nutrition info for Maxim and Carbo-Pro are pretty boring, but here they are anyway:

Maxim Energy Mix

Maxim Energy Mix

  • carb source: maltodextrin only
  • extras: Vitamins C and B1
  • cost per 250ml: $0.32

Carbo Pro

Carbo Pro

  • carb source: maltodextrin only
  • extras: none
  • cost per 250ml: $0.45

The Semi DIY

  1. Infinit NutritionGo to the Infinit Nutrition website.
  2. Complete the online interview (or schedule a phone consultation).
  3. Get your customized formula. Infinit will blend it, put it in a nice little bag, and mail it to you.

Everything is adjustable – flavor, calories, electrolytes, protein, amino acids, and even caffeine. Tell them what you want, and that’s what you’ll get. You could even have different formulas for different swims – perhaps a low-electrolyte formula for a cold ocean swim, and a medium-electrolyte formula for a warm lake swim.

(No, I’m not getting anything for saying this. However, my buddy Jared – who initially brought Infinit to my attention – is sponsored by them.)

Marathon Swimming Nutrition: A product comparison

I hope you’ve enjoyed “Nutrition Week” here at Freshwater Swimmer. As you may have noticed, I’ve been vague about recommending specific products. There’s a reason for that: I don’t believe there’s any single best nutrition plan for all people, in all situations. However, I’ve personally tried a number of sports drink products, and will share my thoughts on them.

Beginning with the low-end market… These products include, but are not limited to: Gatorade, Powerade, and Vitamin Water. Some signs you might be buying one of these products:

  • You can buy it in supermarkets and gas stations
  • It is brightly colored
  • Produced by a subsidiary of a Fortune 500 company, such as Coca-Cola or PepsiCo
  • Advertised on national television and/or billboards
  • Has a flashy, Javascript-heavy website that contains very little actual information.
  • Ingredients lists may be difficult to find. When you do find one, it’s often extensive and includes strange additives like “xanthan gum” and “brominated vegetable oil.”
  • Most relevant to endurance athletes: The primary carbohydrate source is a simple sugar such as sucrose, dextrose, or high-fructose corn syrup (or a combination).


Vitamin Water

Please note: This isn’t an argument about the “morality” of simple sugars. From an exercise perspective, it all ends up as glucose anyway. The issue is osmolality. Because maltodextrin is a larger molecule, it’s easier to consume more carbs without your stomach treating it like food, flooding with water, and causing gastric distress. This might not matter in an everyday workout, but in an 8+ hour swim, it matters.

It’s also easier to control the flavor of a maltodextrin-based drink. By itself, it’s almost tasteless. If you like a sweet, strong-flavored drink, you can always add fructose, fruit juice, or even Gatorade. With simple sugars, the only way to control the flavor is by watering it down – and thus consuming fewer calories.

Continue reading “Marathon Swimming Nutrition: A product comparison”

Marathon Swimming Nutrition: Osmolality and why it matters

On a sunny late morning in Chicago last summer, I told Ted Erikson about the nutrition plan I’d recently used for Tampa and MIMS. Ted EriksonMy plan called for an hourly cycle of two Maxim feeds and one Perpetuem feed. Ted sort of chuckled, and then said something I’ll never forget: “You know, Evan… all you really need is glucose.”

And he’s right: Glucose is the basic unit of energy. Whether you feed on Gatorade or Maxim, it all ends up as glucose anyway. I mention this story because it’s worth remembering as you read what follows. When I said in the previous post that “some carbs are better than others,” I don’t mean that maltodextrin is the be-all-end-all, magical elixir of marathon swimming. It’s not. Many swimmers – including some of the best – have used “simple sugars” to fuel a marathon swim. You can, too!

However, it’s my view (based on both research and experience) that the basic recommendation to an aspiring marathon swimmer – in the absence of strong preferences otherwise – should be a maltodextrin-based fuel. 

One reason is taste – simple sugars are much sweeter than maltodextrin. The neutral-to-slightly sweet flavor of maltodextrin provides much greater control over the final taste of your beverage. However, this is (quite literally) “a matter of taste” and not generalizable. 

Another reason is a bit more obscure. It has to do with how carbohydrates are metabolized in your gut. One important difference between maltodextrin-based sports drinks and sucrose/HFCS-based drinks is their osmolality. I could attempt to explain what this means, but I thought it’d be more fun to get someone who actually knows what he’s talking about.

Brandon SullivanSo, allow me to introduce Brandon Sullivan. Sully is a former teammate of mine on the Columbus Sharks Masters. He is also a certified marathon swimmer, having completed the 2010 USMS 10K Championship in Noblesville. More relevantly, he has a PhD in Biochemistry from (the) Ohio State University!

Sully has generously agreed to explain what osmolality is, and why it matters to endurance athletes. Thanks dude!

* For the record, Ted Erikson’s nutrition plan for his legendary 1967 Farallon Islands swim consisted of “glucose plus anything to flavor and pour, e.g. peaches, pea soup, etc.”

Continue reading “Marathon Swimming Nutrition: Osmolality and why it matters”

Marathon Swimming Nutrition: Art vs. Science

First, a Michael Pollan-inspired minimalist manifesto:

  1. Drink some carbs.
  2. Not too much.
  3. Some carbs are better than others.

One of the most daunting and mysterious aspects of preparing for a marathon swim is planning a nutrition strategy. And for good reason: Nutrition can make or break a marathon swim.

So, aspiring marathon swimmers often seek advice from their more experienced brethren. But how to sort through conflicting information and opinions?

  • Lynne Cox munches on bagels with peanut butter
  • David Barra spikes his drinks with ginger tea and agave nectar
  • Erica Rose chews dried pineapple slices
  • Capt. Matthew Webb favored (I mean, favoured) beef tea and brandy
  • For Janet Harris, variety is the spice of life.
  • Peter Attia has been pounding the table for SuperStarch.
  • Penny Palfrey likes watered-down porridge, and famously once had a tub of chocolate ice cream flown in via helicopter (while playing ‘Stairway to Heaven’ in her head!)

The textbooks aren’t much better:

  • In Dover Solo, Marcia Cleveland recommends “warm, energy-providing liquids, followed possibly by some solid food, or energy gel.”
  • Steven Munatones’ book suggests to “try everything within reason: energy drinks, bananas, sliced peaches, chocolate, and cookies.” He also wisely notes that “what works for another swimmer may not necessarily work for you.”
  • Penny Lee Dean devotes a section to nutrition in her book, but in 2012 her recommendations are a bit dated. A lot has changed in sports nutrition since 1998.

Here’s the thing: In planning your nutrition strategy, you must distinguish the art from the science – the “best practices” from the “special sauce.” Think for yourself. Pay attention to best practices, but don’t eat bagels and peanut butter just because Lynne Cox did.

What are the best practices? Here’s a good start:

Drink some carbs. Your gut processes liquid food faster than solid food.

Not too much. The goal isn’t to replace everything you burn. There’s a limit to how much your body can process at once. A basic hour’s portion of Maxim (or equivalent) provides 58g of carbohydrates, 233 calories, and 750ml fluids (a 7.7% solution). Exceed that only with caution and care.

Some carbs are better than others. Maltodextrin is better than simple sugars* (e.g., sucrose, dextrose, and high-fructose corn syrup). Maltodextrin is the typical carbohydrate source in high-end, “designer” endurance fuels such as products by Hammer, First Endurance, and Infinit (and of course, Maxim and Carbo-Pro).

Simple sugars are the typical carbohydrate source in lower-end, mass-production sports drinks such as Gatorade, Powerade, and Vitamin Water.

Basically, if you can buy it at a gas station, don’t use it on a marathon swim.

And… that’s it. All the other stuff – protein, amino acids, electrolytes – you don’t actually need them (and in some cases you don’t want them). Under certain circumstances, they may help at the margin; but there are risks. Supplemental protein and electrolytes have probably harmed more marathon swims than they have helped. The main thing is to consume carbohydrates – in a form and amount your body can easily digest while swimming. Everything else is just “special sauce.”

Regarding the last point: Why is maltodextrin better than simple sugars? To answer this question, I’ve recruited a special guest author. Stay tuned for the next post…

* Note: I am aware of Peter Attia’s argument that SuperStarch is superior to maltodextrin. That may be true – but I haven’t tried it. I would simply note that Dr. Attia agrees that maltodextrin is superior to simple sugars.

Marathon swimming and low-carbohydrate diets

Following up my previous post on channel swimmer/physician Peter Attia’s webinar about “Nutrition for Open Water Swimming”…

Peter Attia

As you may have heard, the topic of the webinar was broader than the title indicates. In marathon swimming, “nutrition” typically refers to the stuff consumed during a swim to provide energy. But Dr. Attia was more interested in what people eat when they’re not swimming – i.e., diet.

If I could summarize his point, it would be this: Endurance athletes are asking the wrong question. Sure, Maxim is probably better than Gatorade during a swim. But the more important issue is: How best to train our metabolism through diet so it will most efficiently convert fuel into energy. According to Peter (who now has a blog), the ideal solution is a ketogenic diet.

The ketogenic diet is a type of low-carbohydrate diet that restricts carb intake so severely (less than 60 grams per day – equivalent to a small-ish bowl of pasta) that the body is forced to burn fat for energy instead of the “easy” glucose offered by carbohydrates. I won’t get into the theory and biochemical justification for the diet here, but if you’re interested you might consider checking out (in order of sophistication):

The low-carb/paleolithic/ketogenic diet has been around a while – some might even argue, for several million years. (Note: There are subtle differences among the terms low-carb, paleolithic, and ketogenic, but for our current purposes we’ll ignore them.) But what’s intriguing about Peter’s argument is that he’s promoting this diet as an endurance athlete. Even Mark Sisson is quick to note that he’s a former marathon runner.


I actually read The Primal Blueprint a couple years ago – and found it quite compelling. But in the end, I decided against “going primal” because it seemed totally impractical to train for marathon swims without eating lots of carbs. Sounds like bonk city, right? According to Dr. Attia, however, not only can you train for endurance events on a low-carb diet, but you actually have an advantage over your carb-addicted competitors.

The key is being keto-adapted – being able to burn ketones (a byproduct of fat metabolism) for energy instead of glucose. While most people’s bodies are reluctant to transition from glycolysis to ketosis (the scientific term for “hitting the wall”), people who are keto-adapted do it seamlessly. This has important implications for endurance athletes because eventually, all endurance athletes have to burn fat for energy. After 2-3 hours, glycogen stores are exhausted. But if you’ve already trained your body to readily metabolize fat, your energy levels should be steadier through a long swim. At least in theory.

So, will I be hopping on the low-carb bandwagon? Meh…

I’m of several minds about this. On the one hand, I do find the science behind low-carb diets – the benefits for general health and sustainable weight loss – to be compelling. And I do think “primal foods” are delicious. Fresh, organic veggies… free-range eggs… grass-fed beef… dark chocolate… bacon…. What’s not to love?

On the other hand, I really like carbs, too. I’m not sure I want to give up my heaping plate of pesto pasta; an oven-fresh loaf of French bread; tabbouleh salad, hummus, and pita bread; pizza! I’ve also never had any trouble digesting grains – which is a common reason people turn to low-carb diets. And on a practical level, it’s difficult to avoid carbs in most modern societies.

Ultimately, diet is a very personal choice. I wouldn’t advise quitting carbs just for its potential benefits in endurance sports. Personally, I’m not convinced on that point. I used my custom maltodextrin formula on four swims this year, totaling almost 31 hours and more than 90 miles of swimming – and my energy levels stayed consistently strong (shoulder pain was a different issue).

Jonas Colting

Peter presented some interesting data on his own performance benefits from keto-adaptation – but as he freely admits, that’s just one data-point. Ultraman champion Jonas Colting is another interesting data-point. But as far as I know, there have been zero scientifically rigorous, large-sample studies of low-carb diets among endurance athletes.

It’s certainly worthy of further study.

If you do decide to follow in Attia and Colting’s footsteps, you may find the following articles at Mark’s Daily Apple helpful:

One final issue, regarding the weight-loss benefits of low-carb diets. There’s a funny thing about marathon swimmers… many of them actually don’t want to burn off all their fat. Some of them are (the horror!) desperate to gain weight! A little bioprene goes a long way in a cold-water channel. Apparently, Peter Attia has chiseled himself down to 7.5% body fat. Very impressive in most contexts, but probably not ideal for cold water.

Has anyone out there tried low-carb diets? What about during heavy endurance training? What have been your experiences?

On Peter Attia’s nutrition webinar

Yesterday Open Water Source hosted a fascinating web-presentation by Peter Attia, a physician and Catalina Channel solo swimmer. The topic: Nutrition for Open-Water Swimming. Right up my alley, to say the least! There’s good news and bad news.

Bad news first: The webinar was oversubscribed so, despite pre-registering a week ahead of time, I got locked out. The good news: I was able to obtain the audio and slides, and “listen in” after the fact. (Friendly suggestion to the good folks at Open Water Source: Please don’t overbook your webinars. I realize they’re free, but still…)

The even-better news: The webinar was excellent. Though, somewhat different than I expected. A few weeks ago a friend sent me a whitepaper authored by Dr. Attia, entitled “Swimming in the Intensive Care Unit.” The gist of the paper is that a marathon swim is enormously stressful on the body, producing physiological symptoms not unlike those of a patient in the ICU with a traumatic injury. Therefore, proper nutrition is critically important to the success of such an endeavor. His recommendations boiled down, interestingly, to almost exactly what I had discovered on my own:

  • The purpose of feeding during a swim is to supplement your body’s other energy sources (glycogen and fat), not to replace every single calorie you burn.
  • Liquid feeds are better than solid feeds, because solids are difficult to chew and digest while swimming.
  • Feed often – every 15 or 20 minutes – to minimize blood sugar fluctuations.
  • An 8-10% carbohydrate solution (equivalent to, at most, 270 calories per hour) is best.
  • Maltodextrin is a better carb source than dextrose and/or fructose – its lower osmolality is less likely to produce gastric distress.
  • Fluid intake should be enough to require urination at least every hour.
  • Augment the carb drink with protein (or preferably, free-form amino acids) to mitigate muscle breakdown.
  • Do not supplement electrolytes in a saltwater swim (at most, perhaps a small amount of potassium).

Indeed, Dr. Attia’s specific product recommendations corresponded exactly to the products that, independently, I had already found to work best: Maxim and Hammer Perpetuem. So – good for me. Aren’t I smart.

What I didn’t realize until yesterday is that the “Swimming in the ICU” paper is actually outdated! Dr. Attia wrote it circa 2009, but in the past two years has completely changed his thinking and approach to nutrition.

How so? Stay tuned for Part 2