Is Intensity the Key to Minimize Exercise Induced Cravings? What About Workout Duration? What About Sex Differences - Are Women Hungrier Than Men After Workouts?

Next to intensity and duration, sex may be an issue, as well.

On the one hand, you have Dr. Oz and other mainstream sources who say: "Exercise is the key to weight loss! You just make sure you burn an adequate amount of energy everyday and the belly will be gone sooner or later." On the other hand, you will see people like Gary Taubes say: "Whut? Beware of exercise! It's only going to make you hungry!"

A true dilemma! Specifically in view of the fact that both of them can cite studies to support their claims.

If we approach the question a bit less dogmatically, however, it will soon become obvious that neither Oz nor Taubes are "right" or "wrong". Why? Because, as usual, the subject is more complex than the "exercise yes / no" dogma suggests.

You can't "out-exercise" a sloppy diet - don't even try | learn why.

In general, Oz is certainly right: For weight loss to occur, a sustained negative energy balance is required and is typically achieved by decreasing energy intake (i.e. dieting) and/or increasing energy expenditure (i.e. exercising).

Taubes, on the other hand, makes a valid point: In the real world, an increase in energy expenditure is often compensated for by an increase in energy intake.

The optimal exercise regimen would thus be one that burns a hell lot of exercise without having significant effects on the appetite of its practitioners. In today's SuppVersity article we are going to take a look at exercise variables that may influence the effect on appetite, in order to identify the "optimal exercise regimen".

Duration & intensity matter! The longer, the hungrier. The harder, the more satiated?

In one of the most comprehensive studies to date, Erdmann et al. observed in a combined sample
of normal-weight men and women that cycling for only 30 min cycling at either 50 or 100 W had no effect on subsequent appetite ratings and energy intake.

Figure 1: Effects of exercise duration and intensity on energy intake; exemplary study results from Erdmann et al. (2007, left) and Larson-Meyer et al. (2012, right)

After 120 minutes of cycling at a fixed work rate of 50 W, on the other hand, lead to significant increases in energy intake. The problem with Erdmann's study is yet that it was conducted first thing in the morning after an overnight fast. In a "fed" scenario the impact of the exercise duration may have been more significant.

Likewise, not 100% beyond doubt are the results Larson-Meyer et al. (2012) presented in a 2012 study, the results of which would suggest that working out at lower intensities will have, while working out in the "fat burning zone" of ~70% VO2 max won't have significant effects on post-workout (2h) energy intake.
As Deighton & Stensel point out in a recent review (2014), it is however "plausible that the higher percentage body fat and lower VO2 max in the walking group may have confounded the results."In fact, a study by Finlayson et al. demonstrated that body fat and physical activity levels may influence the energy intake response to exercise - at least in females.

The unfitter + fatter, the hungrier! At least in women!?

The scientists from the Institute of Psychological Sciences at University of Leeds analysed the energy intake response to 50 min cycling exercise and separated the participants into two groups: C
ompensators and non-compensators.

Figure 2: Men and women may react differently to exercise; specifically, in men the association between obesity + activity levels and post-workout binges is less pronounced (Finlayson. 2009; Jokisch. 2012)

Compensators were defined as the participants that increased energy intake beyond the energy cost of exercise, whereas non-compensators consumed less energy than that expended during exercise. Analysis of between-group differences revealed a significantly higher BMI and percentage body fat and a lower habitual exercise frequency in the compensators.

What is interesting, though, is that Jokisch et al. were not able to reproduce these results in a recent study with male subjects who exercised for 45 min at 65–75 % of the maximum heart rate and did not respond according to their body fat / weight levels.
Yet even if we assume that obese women run the risk of overeating after workouts. Deighton and Stensel, whose review I referenced previously in this article, were unable to find a single study, where the post-exercise increase in energy intake exceeded the amount of energy that was expended.

The ‘relative energy intake’ is always negative

Or put simply, if the women expend 400kcalper workout and eat 1200kcal instead of 1000kcal on the subsequent meals, they will still have a net deficit of 200kcal.

Table 1: Energy intake during the control and exercise trials of a study investigating the long(er) term effects of exercise on energy intake (King. 2010)

This is particularly relevant, since current evidence suggests that exercise, alone (we are not talking about dieting + exercise, here) won't effect the 24+ energy intake of nine healthy men, who ran for 90 min at  68.8± 0.8% of maximum oxygen uptake  followed by 8.5 h of rest (King. 2010).

Similar effects, ... or rather no effects have been observed by Hanlon et al (2012). for a 24 h period in obese and non-obese women King et al. (1997) in a study on free-living men which analyzed a time-period of 48h, and Pomerleau (2004) in physically active women over a time-period of 72h.
Reference:

• Deighton, Kevin, and David J. Stensel. "Creating an acute energy deficit without stimulating compensatory increases in appetite: is there an optimal exercise protocol?." Proceedings of the Nutrition Society 73.02 (2014): 352-358.
• Drewnowski, Adam, et al. "Food preferences in human obesity: carbohydrates versus fats." Appetite 18.3 (1992): 207-221.
• Erdmann, Johannes, et al. "Plasma ghrelin levels during exercise—effects of intensity and duration." Regulatory peptides 143.1 (2007): 127-135.
• Finlayson, Graham, et al. "Acute compensatory eating following exercise is associated with implicit hedonic wanting for food." Physiology & behavior 97.1 (2009): 62-67. 
• Hanlon, Bliss, et al. "Neural response to pictures of food after exercise in normal-weight and obese women." Medicine and science in sports and exercise 44.10 (2012): 1864-1870.
• Jokisch, Emily, Adriana Coletta, and Hollie A. Raynor. "Acute energy compensation and macronutrient intake following exercise in active and inactive males who are normal weight." Appetite 58.2 (2012): 722-729. 
• King, N. A., et al. "High dose exercise does not increase hunger or energy intake in free living males." European journal of clinical nutrition 51.7 (1997): 478-483.
• King, James A., et al. "Influence of prolonged treadmill running on appetite, energy intake and circulating concentrations of acylated ghrelin." Appetite 54.3 (2010): 492-498.
• Larson-Meyer, D. Enette, et al. "Influence of running and walking on hormonal regulators of appetite in women." Journal of obesity 2012 (2012).
• Pomerleau, Marjorie, et al. "Effects of exercise intensity on food intake and appetite in women." The American journal of clinical nutrition 80.5 (2004): 1230-1236.