Exercise: Does It Really Make You Hungry? The More You Train, The Less Hungry You Are. Still, 30 Min of Cardio Are More Productive Than 60 Min to Get in Shape

Start early and don't stop before you drop. If physical activity is a part of your life from the womb to the grave, you won't have to worry about whether cardio makes you hungry.

Friends of the SuppVersity will recognize this question as a recurring motif: "Does exercise really make you hungry?" An in case you are, you will also know that you have to blame Gary Taubes who seems in all honesty to believe that you would be able to cheat diabesity by simply leaving out the "bad calories" (=carbohydrates) for previous SuppVersity articles such as "HIT the Cravings, Eat Less and Improve Your Health", "Every Dog Has It's Day - Dr. Oz Was Right, Exercise Does NOT Just Make You Hungry" or Facebook News like this.

In the end, Gary is also to blame for today's SuppVersity news, or at least the fact that I jumped right at the results of a recent study from the University of Copenhagen (Rosenkilde. 2013)

So does it make you hungry, or what?

In the Danish capitol, Mads Rosenkilde, Michala Holm Reichkendler, Pernille Auerbach, Signe Toräng, Anne Sofie Gram, Thorkil Ploug, Jens Juul Holst, Anders Sjödin, and Bente Stallknecht conducted what I consider to be a very important study - a study that may not be changing the way we deal with the diabesity epidemic, but one that will hopefully shut those people up, who just tell the lazy ones what they want to hear: "Pah, don't bother about working out: It will just make you hungry!"

Taubes lectures Dr. Oz on "bad calories" = carbs and the perils of exercise

Interestingly, the reasearchers started out with an observation Gary Taubes made as well: "Weight loss induced by endurance exercise is often disappointing." They even come to the same conclusion as Gary did, but realize that their assumption that it may be an "increase in energy intake mediated through greater appetite" (Rosenkilde. 2013) which could explain the failure of previous weight loss trials with a focus on endurance exercise is just that: an assumption - not a given truth and thus from a scientific perspective a hypothesis that requires experimental verifi- or falsification.

When the Rosenkilde et al. recruited 64 sedentary, overweight, healthy young men for their study, they wanted to (ab-)use them to elucidate whether endurance exercise would exert any direct or indirect effects on fasting, postprandial and post-exercise appetite regulation that could precipitate their subjects to overeat and thus confirm Gary's (sorry, Mr. Taubes, I know you are not alone with this message, but you are the one people are listening to)

"Some LISS for MORE" - Do you remember?

SuppVersity Highly Suggested Read: "Some HIIT For Life & Less LISS For More! How to Burn 27,300 Kcal Extra W/out Losing a Single Extra Pound of Fat!" (read full post) - another Rosenkilde study from 2012. And a study in which the Danish researchers were able to show that a HIGH dose of endurance exercise does not produce suprerior fat loss results, even when the energy intake was controlled for and overeating not an issue!

To this ends, the Danes randomized the young men to three groups: A sedentary control group (CON), a moderate dose endurance exercise group (~30min/day; MOD) and a high dose endurance exercise group (~60min/day; HIGH). Now as SuppVersisty veteran you should by now be able to make a prediction about the outcome of the study. Anyone?

I guess you must have forgotten one of my personal favorites, then: "Some HIIT For Life & Less LISS For More! How to Burn 27,300 Kcal Extra W/out Losing a Single Extra Pound of Fat!" (read full article) - an article in which I describe (among other things) the results of a previous study by Rosenkilde that demonstrated quite clearly that a HIGH dose exercise regimen is not more effective than a MEDIUM dose exercise regimen, even if the calorie intake of the subjects was standardized.

The study period in the study at hand were 12 weeks. For the total amount of hours the subjects were running, cycling or whatever other endurance activity they chose was 12x7x30min or 12x7x60min. The exercise had to be performed at identical intensities 66% of the VO2max in all groups and with 66±1% (MOD) and 67±1% (HIGH) all subjects met this criterial.

On a per exercise session basis, the subjects in the HIGH did thus expend more almost twice as much energy as their medium dose counterparts (HIGH: 649±10 kcal vs. MOD: 338±8 kcal; p < 0.001). According to the Taubes'ian logic this must necessarily lead to an increase in appetite and, since there was no dietary prescription as in the 2012 study, a corresponding increase in energy intake.

Note: The the subjects’ adherence to the exercise regimen was excellent, with MOD having only a marginally better compliance to the prescribed amount of exercise than HIGH (MOD: 99±1% vs. HIGH: 96±1%; difference p = 0.047, i.e. non-significant).

So much about "I have not time to go to the gym!"

"Based on each subject’s VO2 max, resting and maximal heart rates (HR) and body weight, the duration of each exercise session was individually prescribed and extensively monitored via requent personal consultations with scientific staff (at least twice weekly).

The exercise prescription was based on each subject’s individual relationship between heart rate and VO2as determined by indirect calorimetry during an exercise test in the laboratory at baseline and was calibrated after the 2 nd , 6 th and 10 th intervention week based on changes in VO2max, heart rate and body weight. Compliance was verified using HR monitors (RS400, Polar Electro OY; Kempele, Finland) that stored information about the subjects’ exercise EE, intensity and duration." (Rosenkilde. 2013)

Both at baseline and at follow-up, the scientists measured the subjective appetite ratings. In addition, plasma ghrelin, glucagon, insulin, peptide YY3-36 (one of the major satiety hormones), glucose, free fatty acids and glycerol were measured during fasting and in response to a breakfast meal and an acute bout of exercise.

Figure 1: Effects on glucagon (goes up, when glucose goes down), ghrelin (hunger hormone), PYY (satiety hormone), and satiety (during breakfast condition), plus effects on body weight and composition (Rosenkilde. 2013).

As you can see in figure 1, the subjects' ad libitum lunch energy intake, which was evaluated three hours after the breakfast meal, did not differ between the endurance exercise groups. Similarly,...

[...d]espite different amounts of endurance exercise, the subjects lost similar amounts of fat mass (MOD: 4.2±0.5 kg; HIGH: 3.7±0.5 kg). Fasting and postprandial insulin decreased ~20% in both exercise groups (P<0.03 vs. CON). [And the a]ppetite measurements were not up-regulated in the fasting and postprandial states." (Rosenkilde. 2013)

So, a high dose of exercise didn't make the subjects hungry. Rather than that, the exact opposite was the case: Fasting and postprandial ratings of fullness and postprandial PYY (one of the major satiety hormones) increased in the HIGH (P<0.001 vs. CON) group to a significantly greater extent than in the supposedly less hungry MEDIUM group and reached a level that "signifies a significant satiety effect" (Rosenklide. 2013) in response to doing 60min of endurance exercise.

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Outliers, over-eaters and general trends: Despite the fact that exercise training may have reduced the hunger and food intake for the majority of the trainees, there were 3 outliers who increased their energy intake almost 4-fold. Accoring to Rosenkilde et al., "[t]hese subjects did not display any adverse subjective appetite ratings immediately before the meal, nor was their satisfaction with the meal apparently different." Personally, I suspect that these subjects may have had blood sugar issues and were borderline hypoglycemic after the exercise. Since that happens quite easily when you cut carbs, but don't eat enough fat (and or too much protein), I guess some of you may this ravenousness very well, right?

When these subjects were excluded from the statistical analysis, the scientists observed a definite tendency towards a decrease in energy intake in the MOD as compared with CON at follow-up (-115 kcal, CI: -244:13; P = 0.08).

Bottom line: Although we should keep in mind that the overall changes in body composition may not reflect the superiority of the HIGH dose exercise regimen on the appetite ratings, hormonal markers of satiety and perceived fullness of the subjects, the results of the study at hand clearly refute the standard hypothesis of increased appetite as the main reason for the failure of endurance exercise based weight loss interventions.

In view of the previously cited results of the 2012 trial by the Rosenkilde et al., it is however not advisable to waste a whole hour of your precious time on endurance exercise everyday. While it is unquestionably possible (I know many people who do it), it's (a) tiring + boring, and most importantly, (b) stressing to jog or bike 60min every day (the stress is probably also the reason for the deterioration of the body fat levels in the 2012 study referenced previously).

In the real world, doing cardio for 60min every day will also reduce the amount of time you have to (1) do your (imho) obligatory resistance training sessions and to (2) shop and prepare whole foods meals. At least for the real busy-bodies it will also (3) steal half an hour (compared to doing less cardio) of your life-time you could better spend sleeping (for both general health and weight loss reasons). Nevertheless, it is not a reason to "overeat" for the average dieter and my personal observations tell me: Those who make it to the gym for their cardio sessions everyday have not the least problem to starve themselves; and the study at hand suggests this may (partly) be because of, not despite doing all that "cardio"!