I am not a fan of referring to the hierarchy of evidence (Haidich 2010, Figure 1) to justify discussing a meta-analysis (in itself a mix of statistical data analysis and, you guessed it, the discussion of individual RCTs and/or observational studies) but I guess in the case of the putative weight-loss benefits of dark chocolate, I can make an exception.
How come? Well, if you do a cursory review of the experimental evidence you will realize pretty soon that the term “conflicting” is not strong enough to describe what you see. Accordingly, I am grateful that a group of Iranian researchers conducted a meta-analysis of all relevant RCTs investigating the impact of cocoa/DC on body weight, body mass index (BMI) and waist circumference (WC).
As the headline already tells you, the results were (imho not surprisingly) negative: Based on the 35 RCTs that were included in the meta-analysis there simply is no effect of cocoa/dark chocolate (DC) supplementation on body weight (-0.108 kg,95% CI -0.262, 0.046 P = 0.168), BMI (-0.014 kg/m² 95% CI -0.105, 0.077, P: 0.759,) and WC (0.025 cm 95% CI -0.083, 0.129, P = 0.640)… Well, unless the scientists restricted their analysis to long-term (4-8 weeks), high-dose (≥30g chocolate per day) studies.
Figure 1: Forest plot of randomized controlled trials investigating the effects of dark chocolate/cacao consumption on waist circumference – beware: the figure doesn’t provide data in cm but as weighted mean difference (Kord-Varkaneh 2018).
This subgroup analysis did indeed produce exactly those results chocoholics will have hoped for: a significant reduction in both body weight and BMI and, more importantly, a non-linear (r = 0.042, P-nonlinearity = 0.008) reduction in waist circumference – with the largest weighted mean difference being observed for a 2008 study by Ried et al. which was originally designed to test the effects of 50 g of dark chocolate with 70% cocoa containing 750 mg polyphenols per day on the blood pressure of prehypertensive subjects (Ried 2008).
There’s no way you’ll get away with eating as much chocolate as you want (assuming you like it): Simply eating as much (dark) chocolate as you can stomach will not, I repeat, it will not get you jacked in no time. Well, the time-aspect should be obvious: after all, only long(er) term studies showed beneficial effects of cacao/dark chocolate on body weight and waist circumference.
As far as the dosing is concerned, it should be highlighted that the dose-response relationship Kord-Varkaneh detected was not linear. In the absence of what I would deem sufficient experimental data, the figure on the left suggests that anything beyond 30-60g per day may do more harm than good.
The time-factor may also explain why more epidemiologic than experimental studies suggest that chocolate consumption is inversely related to body mass index (BMI) and lower body weight and waist circumference (WC) even after adjusting for physical activity, dietary components and energy intake (Golomb 2012; O’Neil 2011).
Figure 2: Meta-analyses of chocolate consumption and risk of diabetes (Yuan 2017).
In all fairness, it should be said that the results differ when the participants total chocolate (not just dark/cacao) is taken into consideration. In that case, the simple truth “more chocolate = more body fat/weight gain” seems to hold.
Did you know that cacao and thus chocolate contains natural stimulants? Plus: The Cacao/Mood Pyramid — In an analysis of the caffeine and theobromine (thought to be responsible for some of the beneficial health effects of cacao | Martínez-Pinilla 2015), Zoumas et al. (2018) found that commercial cocoas contain, on the average, 1.89% theobromine and 0.21% caffeine. Sweet chocolate averaged 0.46% theobromine and 0.07% caffeine, while milk chocolate averaged 0.15% theobromine and 0.02% caffeine. Hot cocoa (chocolate) beverages averaged 65 mg of theobromine and 4 mg of caffeine per 5 ounce serving and chocolate milk prepared from a variety of cocoa‐sugar mixes averaged 58 mg of theobromine and 5 mg of caffeine per 8 ounce serving.
One thing to remember, however, is that cacao is a natural product and even different charges of the same product may contain significantly different amounts and ratios of theobromine:caffeine… and they are as Tuenter et al. point out not the only cacao ingredients responsible for cacao’s/chocolate’s mood-enhancing effects (see the “The mood pyramid” | Tuenter 2018).
That’s probably also why the latest meta-analysis of the effects of chocolate consumption and risk of coronary heart disease, stroke, and diabetes (Yuan 2017) found a progressive dose-dependent increase in diabetes-risk in subjects who consumed more than two servings of chocolate (note: in the absence of subanalyses for dark chocolate, it’s well possible that the threshold may be significantly higher for pure cacao and/or dark = high cacao chocolate).
Figure 3: Ingredient profile of baking, dark and milk chocolate (The Confectionary Foundation).
The latter, i.e. the advantage of high-cacao chocolate may be even more pronounced for the heart-health benefits Yuan et al. observed in the previously cited meta-analysis. Experimental evidence (Rull 2015) does, after all, show that high flavanol dark chocolate will have beneficial effects on cardiovascular function and platelet aggregation. Against that background, it is a pity that …
“[…] due to the lack of data, [Yuan, et al.] cannot conduct stratified analyses by some important confounders, such as total energy intake, body mass index, and types of chocolate products (milk, dark, or white)” (Yuan 2017).
And that’s a problem that’s not specific to Yuan’s meta-analysis. It is a problem that plagues the literature in general. That’s obviously a problem if you take into account the compositional differences between the different types of chocolate as they are illustrated in Figure 3 I borrowed from the website of “The Confectionary Foundation” (original context) as well as the significant differences in micronutrient (esp. phenols) content that’s not visible in Fig 3.
Bottom line: If nothing else, the meta-analysis at hand shows that the study duration and amount of chocolate that was used may explain heterogeneity of previous RCTs, at least partly.
In other words, the meta-analysis teaches us (a) to be patient (effects will take >4 weeks to materialize) and (b) not to hesitate to eat more than a single bar of chocolate (more than 30g that is). Eventually, this shouldn’t surprise you, but I guess with humans always striving for immediate gratification, it may still be disappointing. But don’t worry you can always tell yourself that “dark chocolate” is not 100% cacao and the spoon of Hershey’s you’re putting into your protein shake has, if not weight/waist loss benefits, still proven ergogenic effects (effective dosage 21g/day)
Golomb, Beatrice A., Sabrina Koperski, and Halbert L. White. “Association between more frequent chocolate consumption and lower body mass index.” Archives of internal medicine 172.6 (2012): 519-521.
Kord-Varkaneh, Hamed, et al. “Does cocoa/dark chocolate supplementation have favorable effect on body weight, body mass index and waist circumference? A systematic review, meta-analysis and dose-response of randomized clinical trials.” Critical reviews in food science and nutrition just-accepted (2018): 00-00.
Martínez-Pinilla, Eva, Ainhoa Oñatibia-Astibia, and Rafael Franco. “The relevance of theobromine for the beneficial effects of cocoa consumption.” Frontiers in pharmacology 6 (2015): 30.
O’Neil, Carol E., Victor L. Fulgoni III, and Theresa A. Nicklas. “Candy consumption was not associated with body weight measures, risk factors for cardiovascular disease, or metabolic syndrome in US adults: NHANES 1999-2004.” Nutrition research 31.2 (2011): 122-130.
Rull, Gurvinder, et al. “Effects of high flavanol dark chocolate on cardiovascular function and platelet aggregation.” Vascular pharmacology 71 (2015): 70-78.
Yuan, Sheng, et al. “Chocolate consumption and risk of coronary heart disease, stroke, and diabetes: A Meta-analysis of prospective studies.” Nutrients 9.7 (2017): 688.
Zoumas, Barry L., Wesley R. Kreiser, and Roberta Martin. “Theobromine and caffeine content of chocolate products.” Journal of Food Science 45.2 (1980): 314-316.