What's a Negative Calorie Food?
Stories about "negative-calorie" foods abound. For those of you not well versed in fairy tales, negative calorie foods are those that supposedly take more calories to digest than they provide.
Believers often cite foods like celery, grapefruit, and tomatoes as examples, the reasoning – if you can call it that – being that these foods are so fibrous that your body has to "work" really hard to break them apart and digest them.
While negative calorie foods are possible, in theory, no one's ever found one that actually exists. Of course, if kettlebells had nutritive value and you somehow managed to swallow one, they might end up qualifying as a negative calorie food, but beyond that, there probably aren't any.
Certain nuts, though, might come close to qualifying as "negative calorie" in a roundabout way. While they certainly don't take more calories to digest than they provide, the body absorbs fewer of their calories than the label would suggest.
A recent study also suggests that walnuts and almonds, eaten daily, end up causing your body to lose a surprising amount of body fat, in addition to curbing metabolic inflammation and improving blood chemistry in general.
Scientists found 61 overweight men and women and had them each eat 15 grams of walnuts and 15 grams of almonds a day (as a snack) for 8 weeks. A number of participants dropped out for various reasons, but 48 finished the study.
Participants reduced waist size, hip size, and fat mass, and the "effect size" was impressively large. (Effect size is a statistical tool that allows researchers to describe results more accurately than just saying if something works or not. Instead, effect size answers the more sophisticated question, "How well does something work in a range of contexts?")
The subjects also proved to have adiponectin levels that were about 30% higher than before the study and lipocalin 2 levels that were about 18% higher. The former is a protein hormone involved in the breakdown of fat and the latter is an acute stress response protein involved in inflammation.
The participants also showed a complete revamping of their fatty acid profiles. Saturated fatty acid levels decreased while levels of polyunsaturated fatty acids (PUFAs) increased, particularly the percentages of the favorable omega-3 fatty acids DHA and EPA.
We need to look at one other factor that wasn't discussed in the study but nevertheless plays a role in how almonds (almonds aren't really nuts; they're more closely related to the peach family) or nuts affect the body – it seems the calories they contain end up being overstated a bit because of human physiology.
While the label on a can of almonds might tell you that there are 162 calories in an ounce, it doesn't really pan out that way. Almonds or nuts are notoriously hard to digest so you don't really absorb all the calories. We know this because some of the fat in them goes straight to the feces instead of into your bloodstream (where it would be used for energy or deposited in fat storage tissues).
But some of the nut does obviously get digested and absorbed and the mixed snacks fed to the study participants clearly affected body chemistry and body fat in a number of positive ways. As mentioned, levels of the fat-burning hormone adiponectin went up, as did levels of anti-inflammatory proteins. Blood chemistry improved, as did insulin sensitivity. The combination of all these things led to slimmer, healthier subjects.
To try and duplicate the fat burning effects of eating almonds and walnuts, eat 30 grams of them every day. That equates to about 10 almonds and 5 walnuts (or 10 walnut halves). Just make sure they're raw or dry-roasted and not the greasy kind served with drinks at grandpa's cocktail lounge.
- Cardona-Alvarado MI et al. Almonds and Walnuts Consumption Modifies PUFAs Profiles and Improves Metabolic Inflammation Beyond the Impact of Anthropometric Measure. The Open Nutrition Journal. 2018 Oct;12(1):89-98.