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