Women Have a Hard(er) Time Losing Body Fat W/ Exercise 'cause it Increases Their Appetite More Than Men's, Right?

Is she going to binge after this body weight squat workout? Nah, don't worry...

I've repeatedly written about studies that show that the Taubs'ian notion that "exercise is useless because it just makes you hungry" is bullsh*t. It is indeed useless to work out to burn calories, it is yet never useless to work out - even if fat loss, not health or longevity is your goal.

What you should be aware of, though, is that there is a gender bias in the selecting of subjects in health sciences; and since the average subject in nutrition and exercise sciences is male and studies that have enough male and female subjects to identify relevant sex differences are rare, we don't really know if everything that has been "scientifically proven" can also be considered "scientifically proven" for female dieters and/or trainees.

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The effects exercise will have on your appetite, for example, is such a research interest that has been investigated mainly in male subjects. As Alice E. Thackray, et al. (2016) point out in their latest paper in Nutrients, ...

"[...] opportunities to examine sex-based differences have been limited, but represent an interesting avenue of inquiry considering postulations that men experience greater weight loss after exercise interventions than women" (Thackray, 2016). 

In other words: While we don't know much, the few things we do know about the sex-specific interaction between exercise and your appetite are enough to draw a handful of practically highly relevant conclusions about optimal exercise and diet regimens for women.

Acute exercise, appetite, and compensation with energy intake - it's primarily individual

Before we delve deeper into sex-differences, though, I would like to remind you that the individual differences in fat and weight loss are not just better studied than those between men and women, they are probably also much more relevant than any sex difference - and that in spite of the fact that the research suggests that they are mediated by the same (individual) differences in compensatory behaviours that negate the exercise-induced energy deficit as the inter-individual differences.

Figure 1: The 2008 study by King et al. shows that (a) the individual differences in appetite are magnitudes larger than the actual effect of exercise and that (b) what the subjects make of it in terms of their effects on the subjects' actual energy intake cannot be predicted based on these subjective changes (King. 2008).

In their 2008 study, for example, King et al. found that the individual propensity to compensate for a reduction in energy intake and/or an increase in expenditure can explain weight loss differences that are larger than 50% - albeit with a standard deviation in the "compensators" that is significantly larger than the total weight loss.

SuppVersity Suggested Article: "Training "On Cycle", Done Right - Women See Much Better Results When Periodization is in Line W/ Menstrual Cycle" | read it

Did you know that women benefit from dieting and training in-sync with their menstrual cycle? I am pretty sure you know that as I've mentioned this before at the SuppVersity and even wrote a whole article about "Training on the Female Cycle"evidence  suggests that compared with untailored programs, synchronising diet and exercise training interventions around the hormonal changes that occur during the menstrual cycle elicits greater weight loss (Geiker, 2016) and improvements in muscle strength (learn more). Yet while we do know how cyclical fluctuations in sex hormones (estrogen and progesterone) alter appetite-regulatory hormone concentrations and energy intake in women (Buffenstein, 1995; Brennan, 2009), however, we don't know their interaction with exercise.

Similar discrepancies were found for the effect on subjective hunger, where the standard deviation of the subjects' hunger on a visual analog scale was ±9.6 mm and thus 240x larger than the average appetite increase of 0.4 mm/day. That's huge and it's quite a pity that the study didn't have enough subjects to conduct a meaningful analysis of the effect of the interactions of the subjects' sex on the increase in hunger the subjects experienced in King's 12-week study over the course of which the subjects trained five times a week without having to adhere to an energy restricted diet.

Men or women - that could still make an important difference

That this analysis could have yielded a significant difference between men and women, however, appears to be refuted by studies like Alajmi, et al. whose healthy male and female subjects had - within the previously described inter-individual differences - identical changes in the concentrations of the hunger-regulating acetylated form of ghrelin in response to 60 min treadmill running at 70% VO2peak (see Figure 2) - and that even though the men burned 57% more energy than the women.

Figure 2: Time-averaged total area under the curve (AUC) for appetite ratings (left); and plasma acylated ghrelin concentrations (right) in the control trial (□), and after 60 minutes on the treadmill at 70% VO2peak (■) in Alajmi's study.

In fact, the data in Figure 2 appears to confirm - for both men and women - the anorexic effect that is often ascribed to exercise. The study by Alajmi et al. is yet only one out of four partly contradictory studies that investigate the sex-based differences in the regulation of appetite in response to acute exercise:

• Kawano, et al. (2012) - The first acute exercise and appetite study that compared men and women was published in Obesity Research & Clinical Practice. The authors reported that 20 min of rope skipping exercise increased ratings of subjective hunger 30 min after exercise in women but not men - quite a surprising result, also because high(er) intensity exercise as rope skipping has been shown to be particularly appetite suppressive in the average (=male) study subject; furthermore, Thackray et al. rightly criticize that the authors did not "control for the potential confounding effects of the menstrual cycle, which represents an important consideration for acute exercise studies comparing men and women" (Thackray. 2016). In this regard, recent studies have given us a few interesting insights (see light blue box). However, whether appetite responses to exercise in women are influenced by the menstrual cycle phase is not known and "represents", as Thackray et al. write "a research avenue to consider in the future".
• Hagobian, et al. (2012) - Scientists from the California Polytechnic State University tested the effects on both appetite and energy intake in 11 men and 10 women exercised for 60 min on a cycle ergometer at 70% VO2peak until 30% of total daily energy expenditure was expended (men, expenditure = 975 ± 195 kcal in 82 ± 13 min; women, expenditure = 713 ± 86 kcal in 84 ± 17 min) in a counterbalanced, crossover study.
  

  

  Figure 2: Energy intake (see captions) and macronutrient composition (graph shows %-ages, the figures indicate the actual intake in g) of the post-workout ad-libitum meal (Hagobian, 2012).

  In line with Alajmi et al. (2012) and in contrast to Kawano et al. (2012), Hagobian et al. (2012) found a sign. reduction in energy intake (P < 0.05) after exercise compared with rest in men (672 ± 827, 1133 ± 619 kcal, respectively) and women (−121 ± 243, 530 ± 233 kcal, respectively). A result the scientists interpret as evidence of the previously cited "effectiveness of acute exercise to suppress relative energy intake regardless of sex" (Hagobian, 2012).
• Bailey, et al (2015) - While the previous studies tested relative intense steady state exercises, a 2015 study from the University of Bedfordshire focused on a very different type of exercise. In fact, the 'exercise intervention' consisting of walking a total of 28 min in form of 2 min bouts every 20 minutes was designed to investigate the effect of daily physical activity on appetite and energy intake in 6 male and 7 female inactive, but otherwise healthy subjects, whose appetite and appetite-regulatory hormones were not affected by the exercise intervention.

You probably already suspect it: intensity is a key regulator of the effects of exercise on subjective appetite, but since I've addressed that before while discussing the sex-differences only superficially, I want to refer you to my previous article and focus on the influence of sex of which separate studies in men and women, respectively appear to suggest that...

• 24h energy intake is unchanged in both, men and women in the few studies that investigated this important parameter in male and female subjects in isolation
• acute energy intake (post exercise) mostly remains the same, often decreases and rarely increases in men and women when studied in isolation
• exercise intensity, that's what evidence suggests modulates the effects on energy intake for both, men and women; in that, low-intensity exercise such as walking appears to be more prone to increase energy intake than high(er) intensity exercise such as jogging or sprinting
• dietary overcompensation, i.e. an extra energy intake that provided more energy than the subjects had burned during their workouts, does not occur in either men nor women
• individuality reduce the validity of the results; as previously pointed out, the appetite response to exercise appears to be highly individual and whether that's due to genetics and/or baseline diet (e.g. low carb vs. low fat, etc.) will have to elucidated in the future 

The one thing that's still left to discuss is the chronic effect of exercise on appetite, hunger, the respective hormones and - most importantly - men's and women's energy intakes.

The effects of chronic exercise

Unfortunately, studies that compared the effects of chronic exercise on appetite and food intake of men and women directly, don't exist. What we do have, though, are studies on both men and women (not adequately powered for comparisons), as well as studies that investigate men and women in isolation. These studies suggest that...

• complex interactions w/ weight loss in both men and women - If weight loss occurs in response to chronic exercise, that's, according to King, et al. (2009), because overweight individuals (men and women) balance any potentially existing increased drive to eat due to the extra energy expenditure with a concomitant increase in the satiety response to a meal (increased insulin sensitivity, decreased acetylated ghrelin, decreased leptin | Martins. 2010 & 2013).
  
  Similarly, Thackray et al. conclude in their previously cited review that this interactive effect between exercise, weight loss and appetite / energy intake also explain the complex alterations in appetite-regulatory hormones, of which they even go so far as to say that they "arise as a secondary consequence to changes in body mass" (Thackray, 2016)
• overall, women are more susceptible to changes in energy balance - In the long-term, it becomes more apparent that women react more sensitive to changes in their energy balance. Comparing studies in men and women (direct comparisons don't exist) suggest that this is why women are more susceptible to perturbations in appetite-regulatory hormones and energy intake.
• exercise is less likely to trigger dietary compensation than energy restriction - In contrast to the initially referenced statement of Gary Taubes, it's dieting that makes you hungry, not exercise in both men (King, 2011) and women (Alajmi, 2016). "Dietary restriction," Thackray et al. explain may simply "represent a greater challenge to appetite regulation and energy balance than exercise".
  
  

  

  Figure 3: The energy intake between men and women differed in a 12-week aerobic exercise training intervention in overweight and obese men (n = 35) and women (n = 72), but the effect on the objectively measured (quantified using laboratory-based test meal days) did not differ between the male and female subjects (Caudwell, 2013)..

  And since we know that women react more sensitive to changes in said energy balance, it is not exactly surprising that individual two separate studies by Stubbs et al. (2002a,b) show that only women will compensate ~33% of the extra energy they expended during seven days of daily moderate- or high-intensity exercise (Stubbs, 2002a), while men didn't change their energy intake, at all (Stubbs, 2002b) - at least if we trust their food logs and the subjects' own scales, because that's what Stubbs et al. used as their data source.
  
  That's a problem, because - as usual - other studies suggest an increased compensation in men or, just as one of the few tightly controlled studies in this field no sex- but sign. indiv. differences (Caudwell, 2013). 

Eventually, the jury is thus still out. While anecdotal evidence suggests and evolutionary considerations, i.e. "that women have evolved to store body fat to preserve energy balance and reproductive function" (Thackray, 2016), could even explain an increased energy expenditure in women, the hard evidence we'd need for a definitive conclusion is simply not there.

Not Exercise, But Dieting Makes You Hungry: Beneficial or No Effects on Appetite of Exercise in Lean & Obese. (Ab-) using Exercise to Make Up For Messy Diets Still a Bad Idea! More...

Don't complain, ladies. Use your energy in the gym! As Thackray et al. point out, most of the more recent experimental work "question[s] the prevailing view that exercise is less effective for inducing weight loss in women, with several studies showing equivalent effects of exercise training on body composition in both sexes when the exercise-induced energy expenditure is matched" (Thackray, 2016) - the latter is obviously rarely the case, after all, women have a lower body weight and a lower lean body mass. So even if they trained at the same intensity as men (which a comparison of the average male to the average female gym-goer suggests they don't), they still wouldn't burn as much energy...

Rather than to complain about how unfair life is when it comes to exercise and fat loss, women should use their energy in the gym and focus on the new research on how training and eating according to their menstrual cycle could augment both, their exercise-induced fat loss and the actually desired changes in body composition | Comment on Facebook!

References:

• Bailey, Daniel P., et al. "Breaking up prolonged sitting time with walking does not affect appetite or gut hormone concentrations but does induce an energy deficit and suppresses postprandial glycaemia in sedentary adults." Applied Physiology, Nutrition, and Metabolism 41.3 (2015): 324-331.
• Brennan, Ixchel M., et al. "Effects of the phases of the menstrual cycle on gastric emptying, glycemia, plasma GLP-1 and insulin, and energy intake in healthy lean women." American Journal of Physiology-Gastrointestinal and Liver Physiology 297.3 (2009): G602-G610.
• Buffenstein, Rochelle, et al. "Food intake and the menstrual cycle: a retrospective analysis, with implications for appetite research." Physiology & behavior 58.6 (1995): 1067-1077.
• Caudwell, Phillipa, et al. "No sex difference in body fat in response to supervised and measured exercise." Medicine & Science in Sports & Exercise 45.2 (2013): 351-358.
• Geiker, Nina RW, et al. "A weight-loss program adapted to the menstrual cycle increases weight loss in healthy, overweight, premenopausal women: a 6-mo randomized controlled trial." The American journal of clinical nutrition (2016): ajcn126565.
• Hagobian, Todd Alan, et al. "Effects of acute exercise on appetite hormones and ad libitum energy intake in men and women." Applied Physiology, Nutrition, and Metabolism 38.999 (2012): 66-72.
• Kawano, Hiroshi, et al. "Appetite after rope skipping may differ between males and females." Obesity research & clinical practice 6.2 (2012): e121-e127.
• King, Neil A., et al. "Individual variability following 12 weeks of supervised exercise: identification and characterization of compensation for exercise-induced weight loss." International Journal of Obesity 32.1 (2008): 177-184.
• King, Neil A., et al. "Dual-process action of exercise on appetite control: increase in orexigenic drive but improvement in meal-induced satiety." The American journal of clinical nutrition 90.4 (2009): 921-927.
• King, James A., et al. "Differential acylated ghrelin, peptide YY3–36, appetite, and food intake responses to equivalent energy deficits created by exercise and food restriction." The Journal of Clinical Endocrinology & Metabolism 96.4 (2011): 1114-1121.
• Martins, Cecilia, et al. "The effects of exercise-induced weight loss on appetite-related peptides and motivation to eat." The Journal of Clinical Endocrinology & Metabolism 95.4 (2010): 1609-1616.
• Martins, Catia, et al. "Effect of chronic exercise on appetite control in overweight and obese individuals." Medicine and science in sports and exercise 45.5 (2013): 805-812.
• Stubbs, R. James, et al. "The effect of graded levels of exercise on energy intake and balance in free-living men, consuming their normal diet." European journal of clinical nutrition 56 (2002a): 129-140.
• Stubbs, R. James, et al. "The effect of graded levels of exercise on energy intake and balance in free-living men, consuming their normal diet." European journal of clinical nutrition 56 (2002b): 129-140.