Friday, March 18, 2016

Hold The Carbs At Dinnertime? Wait. What?!


It's time to get serious... seriously trained that is.

For those of you who love to read anything and everything about food you may have recently read an article by Gretchen Reynolds of the NYTimes titled For Serious Training, Hold the Carbs at Dinnertime. The article specifically addressed a strategic plan around skipping carbs all together at the evening meal as it may improve athletic performance in events following the meal.  Sounds like a little too much planning ahead, a little too risky, or something that perhaps you are already doing? (You trend-setter you). Here are a couple of basic points from my professional opinion both in regards to this article and to sports nutrition in general.


  • There is no ONE ideal sports diet- we are not all built in a box and whereas there are guidelines there are some flexibility within these guidelines in regards to the type of sport as well as the genetics of the athlete  

  •  Some may think that dietitians advocate for “heaps” of carbs at the dinner table for athletes that is not always and necessarily true. Carbs are very important as they are the body’s first go-to source of energy, and they are also stored as glycogen for use of energy when blood sugar levels run low. Plus the whole carb loading concept, while it may have been something pushed by coaches in the past, may cause issues such as greater water retention and therefore temporary weight gain cramping your running style, digestive discomfort from high fiber foods and blood sugar changes, which is especially dangerous if you are have diabetes. 

    So when you burn out of carbs what is next in line? Fat. Which is preferred over protein as we want to hold onto that precious protein for other uses such as healthy hair, nails, muscle growth, and more (see my previous post How Do I Know If I Am Getting Enough Protein? for more information)

     Let us delve a little further into this shift from carbs to fat for fuel- particularly the main source of fuel for your body. When we do this we are forcing our bodies to completely undue their natural progression of burning energy for fuel. I am not saying this is wrong, and I am not saying it is right- I am just saying that it may be  person specific. Science is proving that  some diets work better for some then for others and are gene-specific as well as based on the condition of the person. I will comment that this specific diet manipulation may even be dangerous if applied long term as more studies are needed. On a lighter but nevertheless well understood note, without enough carbs you may start to get a little, ummm, hangry.

     But what is all this danger talk about you ask? Great question! The body just doesn't switch from burning carbs to fat and say “ok this is cool I will now use fat and no need for more carbs.” It has to train and get used to it. During this short term training it could be a drag for the bagel loving runner. Also, lets keep in mind that without that “quick energy” streaming through your body from a handful of raisins or a banana the more one may struggle to finish the race strong.

     The study that the NYTimes article was based on was conducted in Paris, France after researchers from the French National Institute of Sport, Expertise and Performance and other like-minded institutions got curious about the “sleeping low” sports diet where an athlete skips carbs at dinner time (see ya bread bowl) and trains with a low availability of carbs. It takes about 12 hours for the liver to run out of glycogen so when you pass on the carbs at dinner you are most likely past the 12 hour mark.

Here are some key points about the study published in the Medicine and Science in Sports & Exercise Journal:

  • 21 experienced competitive male triathletes participated in the study 
  • Subjects were tested via a simulated triathlon to test out their pace and fitness level
  • 50% of the subjects were randomly chosen to eat a “standard sports diet” and the other half on a “sleep-low diet"
  • The same amount of carbs were consumed over the course of the day (6 grams/kg of body weight for each person in each group -this means for a 170 (77 kg) person he is consuming 462 grams of carbs a day 
  •  The distribution of carbs for the 2 groups differed by restricting carbs in the evening and piling them on in the morning for the sleep-low group vs equaling distributing carbs throughout the day for the control group.
    I think by now you are having an "aha" moment.Technically, the sleep-low group was not consuming  less total carbs in a 24 hour period, and it was that they were only restricting during one part of the day and making up for it the next morning.  

 Now back to the study.

  • The “sleep-low” folks went through 3 trials of diet/training cycling interventions for 4 days a week for 3 weeks with low impact activities on the off days. The training sessions were completed in the afternoon to deplete carbohydrate availability before dinner.
    • The first intervention included "train-high" interval sessions of high intensity in the evening with high-carbs after training
    • The second intervention included the same type of training but this time with  overnight carb restriction ("sleeping-low")
    • The third intervention switched from high intensity to  "train-low" sessions with a low amount of carbs available endogenously and exogenous-ly- that's science speak for low stores of carbs in the body in the form of glycogen and a low amount of immediate energy from carbs consumed during the training
  • As for the control group they followed the same training program but with high amounts of carbs available at all times (6 grams/kg body weight/day) - no restrictions overnight and no restrictions during exercise

    The sleep-low guys ate virtually all of their carbs at breakfast and lunch. The control group  ate carbs at all meals with the key meal being carb repletion at dinner time. In the morning before breakfast the subjects  cycled for an hour at moderate pace.  The sleep-low group was pedaling away their little carb reserve and relying on fat whereas the control group had more carbs in the form of glycogen to depend on before transitioning to fat only utilization.

      Put back to the test of the simulated triathlon and the sleep-low group showed improvements in both cycling efficiency during moderate cycling and to exhaustion. Futhermore they performed 3% better during the 10K run. Over a minute faster at finishing the race vs the control group! Last, but not least, the sleep-low group lost more body fat vs the control group.

So what does this all mean to the athlete who is looking to improve performance, or perhaps to lose greater amounts of fat mass?

  • Strenuous exercise in the afternoon followed by deprivation of carbs ( I know I am already crying) and then waking up to a casual training session followed then by a carb heavy breakfast (now I am happy again) does show some promising results to improve endurance performance
  • In 3 weeks it appeared as though athletes were able to access fat for fuel, which allowed them to work harder, condition better and gain more speed

This next insert comes directly from the  NYTimes article itself that I want you ALL to pay special attention to:

“Such a rigorous routine is not for everyone, of course. Those of us not training for a marathon, triathlon or similar event probably would not enjoy or benefit from sleeping low. Even serious athletes should thread the approach into their training cautiously, Ms. Marquet said, beginning a few weeks before a race and easing off in the days just before the event, when they should down carbohydrates at will.”

Ms. Marquet, the leading researcher in this study, also gave word that MOST of the athletes have now integrated this sleep-low diet  into their training. But before you run off (literally and figuratively)and start making reservations as steakhouses for dinner here is the final conclusion from the researchers themselves:

"Short-term periodization of dietary CHO (carbs) availability around selected training sessions promoted significant improvements in sub-maximal ( cycling at less then their best) cycling economy, as well as suprea-maximal  (cycling faster then before) cycling capacity and 10 km running time in trained endurance athletes.” 

Yes, parenthesis were  added by moi.

......and now some poetry in motion, all pun intended.
Carbs were restricted at dinner only
But without these carbs the athletes felt lonely
However, their performance improved, deeming them the winners
But it was still hard foregoing those carbs at dinner.
All joking aside, here is....

My Takeaway:  

     We must always use common sense and just because a study is highlighted in a very well known publication it does not mean that all people training for a strenuous event must now follow the no-carb-at-night-tactics because it is may not be the best fit for everyone. This study had some limitations as all studies do. Only males were included in this study and they were already endurance trained athletes. The intervention blocks were only 3 weeks in length which brings to question if this diet is even attainable over a longer period of time. This is important to note since training periods for triathlons and marathons are much longer then 3 weeks. This kind of diet may be better when done towards the end of training. Finally, the nutrition intervention, although given in specific directions, was self reported by a detailed food diary the subjects kept with them. This is a common limitation to many studies and does not make this study dis-credible, only one to have an open mind about before committing to it.

    I recommend that athletes work with a Registered Dietitian-Nutritionist who specializes in sports nutrition if they plan on implementing this diet into their training for optimal safety and greater personalization.

Kelly Ahearn, MS RDN CDN is Founder of Indigenous Nutritionist, a private practice and consulting startup based in NYC. She has partnered with Running This World to offer nutritional education sessions via tele-health for anyone who registers for the complete package at - website is coming soon!


Marquet LA1, Brisswalter J, Louis J, Tiollier E, Burke LM, Hawley JA, Hausswirth C. Enhanced Endurance Performance by Periodization of CHO Intake: "Sleep Low" Strategy. Med Sci Sports Exerc. 2016 Jan 7.  [Epub ahead of print]        
Reynolds G. For Serious Training, Hold The Carbs At Dinnertime. March 9, 2016 5:25 am New York Times Well. Accessed March 16, 2017.

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