Without naming any names, there are a lot of places where you can get lists of "superfoods" that “blast fat” or “bust your gut” or do some other kind of weight-destroying magic described in language so violent it gets a little disturbing if you think about it too closely. The promise of superfoods is the promise of Just One Thing: regardless of what the rest of your diet and lifestyle look like, this one seed or berry or leaf will have a dramatic effect all by itself.
But if you take a look at the studies on superfoods, you might start noticing something a little funny: a lot of them aren’t all that impressive. So while we’re getting violent about “burning” and “blasting,” here’s a head-to-head battle between sleep and superfoods. Based on studies in humans (not test tubes, rats, or mice) eating actual food (not purified extracts or pills), how do superfoods stack up against the simple, old-fashioned trick of getting enough sleep?
Direct Measurements of Weight Loss
Here are a couple studies on superfoods and weight loss:
- Chia seeds: in this study, chia seed supplements for 12 weeks made no significant differences in body weight or body composition.
- Garcinia cambogia: in this study, Garcinia cambogia was no better than placebo.
- Green tea: this Cochrane review examined the effects of green tea on weight loss. Studies outside Japan found an average of 0.04 extra kilograms lost; studies inside Japan were too different to combine the results. The review concluded that “Green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults” with no effect on maintenance.
The superfood-induced weight loss isn't terribly impressive. Now for the sleep. It’s hard to find intervention studies on sleep that last as long as the diet/supplement studies. Ensuring sleep deprivation every night is probably more labor- and money-intensive than just giving everyone a pill to take every day and sending them home. What we do have are shorter-term studies and association studies:
- In this study, insufficient sleep for just 5 days caused a 0.82 kilogram (1.8 pound) weight gain, even though the subjects weren’t hungrier. Now imagine that extended out to a stressful 6 months or a year.
- Many other studies have shown associations between sleep quality and weight loss. For example, in this study, researchers looked at women on the same weight-loss program. They measured their sleep quality before the study started, and at 6 months. Women with good sleep quality and at least 7 hours/night had a 33% greater chance of successfully losing weight than women who slept poorly or not enough. Successful weight loss here was defined as 10% of their body weight or more at 6 months. Because they measured sleep quality at the beginning of the study, this study avoids the problem of reverse causation
It’s frustrating that we don’t have the kind of long intervention studies where subjects stay in a sleep lab every night for several weeks, but it does look like sleep is coming out ahead here.
Insulin, Hunger, and Other Contributors to Weight Loss
Another way to compare sleep and superfoods for weight loss is to look at short-term effects that might indicate a benefit in the long run. One example is insulin sensitivity: if something improves insulin sensitivity, it will probably be beneficial for weight loss down the line. These effects are easier to measure after just one or two nights in the lab, so it’s easier to compare them.
On the superfood side:
- Cocoa: This study gave subjects a fast-food breakfast (points for real-world accuracy!), with either a placebo drink or by an
antioxidant-rich cocoa beverage. The cocoa increased insulin levels but had no effects on insulin resistance or blood glucose.
- Green tea: This study found significant differences between green tea and sour tea (a different kind of tea) on insulin sensitivity…because the sour tea actually impaired insulin sensitivity, not because the green tea had a big benefit. This one found no effect of green tea on insulin or glucose response to a meal.
- Flax seeds: studies are conflicting. This study found no benefit; this one found it helped; this one found a benefit from a moderate amount but not a higher amount.
To compare that with sleep, take a look at this study. People without diabetes or other metabolic disease got slammed with just one night of sleep restriction (4 hours as opposed to their regular 8). The sleep-deprived subjects all had worse insulin sensitivity. The authors concluded that “Partial sleep deprivation during only a single night induces insulin resistance in multiple metabolic pathways in healthy subjects.” That’s much stronger evidence for sleep as an insulin-sensitizing intervention than it is for the superfoods.
Hunger, Appetite, and Cravings
On the superfood team, we’ve got…
- Garcinia cambogia: this study gave overweight women on a diet either Garcinia cambogia or placebo before meals. There was no difference in hunger, appetite, dietary compliance, or weight between the groups.
- Flax: This study found that a flax drink reduced subsequent food intake compared to a control drink by 67 calories, but if you wanted that amount of fiber from actual flax, you’d be eating about 47 calories of flax, so the net benefit is only around 20 calories.
- Green tea: this study found an effect on satiety after one meal, but a long-term study found no effect.
Sleep has also been studied for its effects on hunger. Here’s one study. The researchers found that sleep deprivation reduced people’s ability to evaluate their food choices while increasing brain activity in regions that motivate consumption. Sleep-deprived people wanted more calorie-dense foods, and if they’d eaten everything they wanted, they would have eaten an extra 600 calories per day, on average.
So far, the evidence suggests that getting enough sleep is a better hunger-reducer than the superfoods.
Superfoods have antioxidants, and antioxidants protect against inflammation, right?
- Chia seeds: did not change inflammatory markers over a 12-week period of supplementation. This study found that they did, but the chia group also ate a different diet (lower in carbs).
- Cocoa and cocoa antioxidants: this review looked at the effects of products containing cocoa polyphenols and inflammatory markers. Results were conflicting and inconsistent – if you look down the table of study data that they collected, the words “no effect” keep showing up. The researchers note that more studies are needed, but so far, it’s not terribly impressive.
- Flax seeds: this study found that they had no effect on inflammatory markers in people with prediabetes, and this one found the same in obese people with blood sugar problems.
- Green tea: the title on this one says it all: “Green Tea minimally affects Biomarkers of Inflammation in Obese Subjects with Metabolic Syndrome”
Guess what has a stronger effect on inflammation? Sleep! This meta-analysis of many different studies found that sleep disturbance in general (either too much or too little) was associated with higher levels of the inflammatory markers C-reactive protein and interleukin-6. The individual results varied slightly from study to study, but compared to any of the superfoods above, the evidence for inflammation is on the side of the sleep
Summing it Up
None of this is an argument that superfoods are "bad." There’s nothing wrong with these foods just because they don’t magically make you thin. Most nutritious foods have no magical obesity-preventing powers, because that's just not how individual foods work. The point is that "superfoods" don't look much different from regular nutritious foods in this particular respect. If you want big changes in your body, individual "superfoods" aren't powerful enough to override all your other diet and lifestyle patterns. The superfood myth of Just One Thing isn't supported by these studies.
This gets very obvious when you compare the "superfoods" to sleep. At least from the studies we have, sleep appears to have a much more powerful effect on weight and metabolic health than any one particular food.
One important caveat is that many of these foods have few or no studies in humans in diet-relevant amounts. It’s possible that new studies will completely change the comparison. But based on the evidence we have now, sleep looks a lot more “super” than any of these foods.