According to the Chicago Tribune:
"Test subjects ate more after (two different types of) water immersions than they did after sitting in a chair.
Average calorie intake per person after the cold water immersion was about 489, and about 517 after the tepid water immersion. After resting in a chair, average calorie intake was about 409.
Researchers found lower levels of leptin and higher levels of ghrelin after both water immersion experiments. Following water immersion more carbs and protein were eaten as well."
Since the study included only 10 participants, researchers suggested that further studies be done with larger sample sizes. The study was published in the Medicine & Science in Sports & Exercise.
I've discussed the variables that can boost or hinder the benefits of your exercise routine in a number of previous articles, and I'll summarize them again below, but this study is unique in that it shows how your choice of cool-down routine can affect your post-exercise appetite.
Jumping into the pool after strenuous exercise can feel heavenly, but according to these preliminary findings, you may want to reconsider taking that dip if you're trying to lose weight.
The study was limited to 10 participants, so it may be premature to draw concrete conclusions. But if you're trying to shed a few pounds, these recommendations may be worth considering.
The participants were evaluated three times. Each 40-minute run was followed by one of three different 20-minute cool-downs:
- Immersion in cold water (59 degrees Fahrenheit)
- Immersion in tepid water (91 degrees Fahrenheit)
- No immersion; sitting resting
After each test, they were served a buffet breakfast and allowed to eat as much as they wanted.
Blood samples were collected to evaluate blood glucose, lactate, and the appetite-regulating hormones leptin and ghrelin.
Interestingly, after water immersion, the subjects:
- Consumed an average of 80 to 108 more calories
- Consumed more carbs and protein
- Had reduced leptin levels
- Had increased ghrelin levels
Leptin plays a role in decreasing your appetite while ghrelin tends to increase it, so the changes in both of these hormones post-water immersion are indications of increased appetite, or reduced satiety.
Granted, more research is needed to confirm these findings, and it's possible that cold water immersion causes other metabolic changes that may counteract the slight increase in calorie consumption...
Not sure how I will apply results of this research personally though. In the summer months when I do my Sprint 8 exercises I am drenched in sweat and typically find it very relaxing to jump in my in-ground outdoor pool. Since I really don't need to lose any weight, I will likely continue the practice as I find it refreshing. I will not even have the choice though until next May.
Aside from abstaining from a dip in the pool, there are a number of other pre- and post-exercise strategies you may want to keep in mind in order to boost your weight loss potential and optimize the health benefits of exercise.
Remember, exercise changes your biochemistry, and you can aid or hinder these beneficial changes, depending on what you chose to eat before and directly after exercise.
Fasting Prior to Exercise Forces Fat Burning
You may have heard that exercising on an empty stomach will help burn more fat, and there seems to be some truth to that, although it might not be appropriate for everyone.
Exercising vigorously when you're blood sugar is low could lead to dizziness and poor performance, and exercising while hungry can also lead to overeating afterwards.
Personally, I believe the best approach is to use some common sense and listen to your body. For example, if you feel weak or nauseous while exercising on an empty stomach, you may want to at least eat a small meal before exercising.
That said, the reason why fasting before exercise seems to work is because the fat burning processes in your body are controlled by your sympathetic nervous system (SNS). The SNS is inherently activated by exercise and lack of food. The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP Kinases), which force the breakdown of fat and glycogen for energy.
So, when you exercise on an empty stomach, you're actually forcing your body to burn fat.
The Ideal Pre-Exercise Meal to Boost Fat Burning
However, as I just mentioned, fasting prior to exercise can reduce your performance. Fortunately, there is a better, and probably more efficient, way to boost fat burning without fasting.
A recent study published in the journal Medicine and Science in Sports & Exercise found that consuming 20 grams of whey protein 30 minutes before resistance training can boost your body's metabolism for as much as 24 hours after your workout.
It appears as though the amino acids found in high quality whey protein activate certain cellular mechanisms (mTORC-1), which in turn promote muscle protein synthesis, boost thyroid function, and also protect against declining testosterone levels after exercise.
In practical terms, consuming 20 grams of whey protein before exercise and another serving afterward will most likely yield the double benefit of increasing both fat burning and muscle build-up at the same time.
One of the worst foods you can eat prior to exercising is carbohydrates, as carbs will inhibit the SNS and reduce the fat burning effect of your exercise. Instead, this type of meal will activate your parasympathetic nervous system (PSNS), which promotes energy storage—the complete opposite of what you're aiming for.
Personally I do strength training three times a week and will typically consume a whey protein meal one hour before, one hour after, and three hours after, to provide the fuel for muscle growth. This is not as necessary for non-strength training exercises, however.
Foods to Avoid After Exercise
So, fasting, or even better, consuming high quality whey protein prior to exercise can boost fat burning. But equally important is what you do afterwards.
Again we find that sugar is at the bottom of the list.
In fact, consuming sugar (including starchy carbs that convert to sugar, and sugary energy drinks) within two hours of high intensity Sprint 8 exercises will negatively affect your:
- Insulin sensitivity, and
- Human growth hormone (HGH) production
Both of these factors are very important for optimal health and longevity.
Impaired insulin sensitivity (insulin resistance) is the underlying cause of type 2 diabetes and a significant risk factor for other chronic diseases such as heart disease.
Meanwhile, maintaining your HGH levels (which tend to drop off after the age of 35) will help keep your body strong and your health robust.
The beneficial impact of a low-carb post-exercise meal on your insulin sensitivity was recently confirmed by a study published in the Journal of Applied Physiology. And hghmagazine.com clearly explains how consuming sugar/fructose, including that from fruit juices, within this two-hour window will decimate your natural HGH production:
"A high sugar meal after working out, or even a recovery drink (containing high sugar) after working out, will stop the benefits of exercise induced HGH. You can work out for hours, then eat a high sugar candy bar or have a high sugar energy drink, and this will shut down the synergistic benefits of HGH.
… If you miss reaching HGH release during working out, you will still receive the calorie burning benefit from the workout. However, you'll miss the HGH "synergy bonus" of enhanced fat burning for two hours after working out.
This is an extremely important fact to remember if you want to cut body fat and shed a few pounds.
So, to further reduce body fat while enhancing your insulin sensitivity and promoting HGH production, you'll want to eat a low-carbohydrate meal within that two-hour window.
One of the explanations for why a low-carb meal after exercise works is because carbs prevent the production of the hormone somatostatin. One of the primary purposes of this hormone is to inhibit the production of human growth hormone. So, by reducing somatostatin, you're not hindering HGH production.
Fitness expert Phil Campbell further explains how you can maximize your HGH production by limiting sugar intake for two hours post exercise, in this article on HowToBeFit.com.
Are You Exercising Effectively for Weight Loss and Longevity?
Since I've just discussed HGH, I want to remind you that there is only ONE specific type of exercise that promotes the production of HGH in your body, and that is high-intensity interval training such as Sprint 8.
Virtually all exercises -- certainly most conventional cardio or standard aerobics -- fail miserably when it comes to increasing growth hormone. Sprint 8 exercises, however, are proven to boost natural HGH production.
Sprint 8 type exercises can also dramatically improve your cardiovascular fitness and fat-burning capabilities in a fraction of the time. For more in-depth information about Peak Fitness exercises, please see this previous article, as it is very important to perform these exercises properly.
Clearly, if you decide to use the only type of exercise that will increase growth hormone, then it would be a shame to wipe out this great fantastic benefit with foolish food choices like sugar/fructose/carbs.
Now, there is a minute group of elite and professional athletes who are actively competing and therefore less concerned with increasing growth hormone than with performance. For these athletes, consuming some carbs, preferably dextrose-based, during the two-hour recovery phase is probably a good idea in order to improve their recovery time.
But for the average person, forfeiting the benefits of HGH is both unnecessary and unwise.