Study under review: Extended calorie restriction suppresses overall and specific food cravings: a systematic review and a meta-analysis.
Throughout most of our evolutionary history, we have had extremely limited access to calories. To ensure our survival, we were conditioned to seek out and enjoy eating high-calorie foods. For this reason, scientists have suggested that the highly palatable foods abundant in today’s world can hijack our brain’s reward system. This could play an important role in obesity, as the reward system is intimately linked with food learning, food preference, and perhaps food cravings.
Food cravings are the desire for a specific type of food. There are two broad theories regarding how they form. The first theory is that food cravings emerge due to energetic or micronutrient need. This idea seems intuitive; we often feel that we should eat ‘what our body needs’, and if the body is signalling that it’s low in some nutrients that a specific food has, the body will tell the brain what it needs, and the brain will create a craving for that specific type of food.
The second theory is the idea that food cravings emerge due to pairing consumption of specific food types with a particular rewarding stimulus. For example, if someone consistently satisfies their hunger with pizza, eating pizza will be rewarded, and a craving for pizza will result in the future, since the brain learns that pizza makes hunger go away, even though any food would have done the trick. This type of craving formation has some support from one study which had people satisfy their hunger with only chocolate, while it had others eat chocolate only when full. The study found that those who ate chocolate to satisfy hunger developed cravings for chocolate, but not people who ate a similar amount of chocolate only when full. Pairing eating with other rewarding stimuli may also lead to the formation of food cravings. For instance, if someone eats around family a lot and they enjoy it (or enjoy the lack of grief they get from not taking a second serving of grandma’s lasagna), they’ll crave similar when they see their family in the future.
In short, this theory states that food cravings may occur for a reason similar to why Pavlov’s dogs wound up salivating at the ring of a bell. When feeding the dogs, Pavlov also rang a bell. After a while of this, the dogs associated bell-ringing with tasty treats. Then, if the bell was rang, the dogs salivated, even if food wasn’t present. This salivating is known as a “conditioned response”, since the dogs are conditioned over time to associate bell-ringing with food. The second hypothesis for the origin of food cravings similarly suggests that they are largely a conditioned response. This suggests eating motivation is the product of environmental, social, and contextual cues, in addition to features of the food itself. The process of how food cravings could form according to this theory is summarized in Figure 1.
The question is: which of these two hypotheses is correct? Evidence exists in both directions. The deficiency hypothesis is thought to be supported by the phenomenon of rebound weight gain; it’s reasonable to think that cravings would get stronger as the body senses deprivation of certain nutrients, since food intake is being cut. This hypothesis is also consistent with some evidence suggesting that caloric restriction increases food cravings over the longer term. On the other hand, there is also some evidence that calorie restriction of at least 12 weeks could lead to the suppression of food cravings, lending credence to the idea that cravings may indeed be a conditioned response, since cravings fall if they aren’t reinforced by giving in to the urges.
In the meta analysis under review, scientists conducted a broad literature search of previous investigations where participants’ self-reported craving was measured both before and after a calorie-reducing intervention. Their main goals was to examine whether reducing caloric intake can reduce, or evoke, a greater desire for food.
Food cravings are a desire for a specific type of food. There are two main hypotheses concerning why these urges arise. One theory is that they come from biological signals that the body is lacking in certain nutrients. This suggests that food cravings will probably not subside over time as long as the nutrient desired is lacking. The other is that they are more psychological; they arise, at least in part, from associations with other rewarding stimuli. This suggests that food cravings may decrease with time if not reinforced. The aim of the meta-analysis was to examine how food cravings responded to calorie-restricted diets to see which theory the evidence is more in line with.
Other Articles in Issue #36 (October 2017)
Interview: Kelsey Kinney, MS, RD
Registered dietitian, blogger, and podcaster Kelsey Kinney shares her wealth of knowledge about how gut bacteria can impact digestive health, and discusses how the concept of functional medicine plays a role in her work.
Interview: Brad Schoenfeld, PhD, CSCS
Have questions about load’s effect on hypertrophy, supplements with the strongest evidence base, and effective weight loss strategies? Researcher and renowned body composition expert Brad Schoenfeld has answers.
Lifting the weight of anxiety
Aerobic exercise has been shown to be moderately effective for reducing anxiety. Does resistance training have similar benefits?
Blood sugar and spice
Cinnamon’s been used for medicinal purposes for millennia. Research from the past few decades suggests it may also be useful for controlling blood sugar. But is it?
Be the tortoise or the hare: it doesn’t matter for fat loss
Interval training and moderate-intensity aerobic exercise can affect the body in different ways. But do these differences extend to fat loss?
Antioxidants for the eyes: can they prevent or delay age-related macular degeneration?
AMD is a major cause of vision loss, and may be tied to the high amount of oxidative stress the eyes undergo. Some antioxidants could help delay its progression.
Something smells fishy: is your fish oil oxidized?
Previous research found that a lot of fish oil being sold in New Zealand was subpar. Newer research out of Australia says otherwise.