In order to reduce body weight, an energy deficit needs to be in place, and this state can be accomplished through a wide variety of strategies. An extensive amount of research over multiple decades has showcased that a number of nutrition approaches can induce weight loss, however, the current prevalence of excess adiposity suggests that new and unique approaches are needed to increase weight loss maintenance success.
A typical issue with the dieting process is an incremental increase in appetite as body weight decreases. While there are ways to attenuate this effect, it cannot be prevented. The cornerstone nutrition interventions to curb appetite include increasing protein and fiber intake. Another commonly recommended strategy is pre-meal water consumption .
In combination with these tried-and-true methods, emerging evidence suggests that altering expectations is an area that deserves serious consideration. For anyone who has undergone an intensive fat loss phase, this intuitively makes sense. As portion sizes inevitably decrease over time, one might look at a plate of food and conclude that it will have little effect on their raging appetite before even taking a bite.
If we can alter these expectations, and create the belief that the impending meal will generate a high level of satiety, this could bolster dietary adherence and improve long-term outcomes.
In this fascinating trial, we gain some insight into the efficacy of this hypothesis. The researchers tested the effect of expected satiety (ES) on total ghrelin response and subjective markers of hunger and fullness following two breakfast test meals. They also measured the subjects’ intake at an ad libitum lunch and required them to keep a food journal for the rest of the day in order to measure total energy consumption.
The experiment utilized a within-subject design (i.e., all subjects were observed under both conditions). Subjects visited the testing facility on two separate occasions one week apart.
In each arm of the trial, the subjects consumed a breakfast test meal of an egg and cheese omelette containing three medium eggs and 45 grams (g) of cheese.
In the “small” condition, subjects were under the impression that they were receiving a two-egg omelette with 30g of cheese. In the “large” condition, they thought the omelette was made with four eggs and 60g of cheese. Again, in reality, the omelette they consumed in both interventions contained three medium eggs and 45g of cheese.
Prior to consuming the test meal, the perceived contents of the meal were displayed on a monitor. This allowed the subjects to conceptualize the quantity of ingredients they were theoretically receiving to further mold their expectations.
After receiving the test meal, subjects were asked to taste the omelette, imagine eating the whole thing, and then think about how long they would expect it to stave off hunger.
Following the consumption of the omelette, subjective appetite and total ghrelin levels were measured for the next four hours at multiple time-points (30, 60, 120, 180, and 240 mins). Participants were then given access to a pasta and tomato sauce lunch and told to eat as much as they liked.
As the subjects exited the facility, they were given a food scale, along with pen and paper, and instructed to record their food intake for the rest of the day.
Unsurprisingly, when participants thought they were about to consume a four-egg omelette with 60g of cheese (i.e., the “large” condition), they expected it to deliver more satiety.
For reported hunger, while differences were not statistically significant, the data trended toward greater levels of hunger in the small condition at all time points, with robust differences at 120 and 180 mins following the breakfast test meal. However, there were no significant differences in total ghrelin response between interventions.
In regard to overall energy intake, when subjects thought they consumed a large omelette, they ate approximately 70 fewer calories (kcal) at the pasta lunch.
Furthermore, assessment of the participants’ food diaries indicated that when they were in the large condition, they went on to consume an average of 1022 kcal for the rest of the day, which was 97 kcal less than when they were in the small condition (1119 kcal).
Overall, subjects consumed about 167 fewer kcal over the course of the day when they thought they started off their day with a large omelette rather than a small omelette.
These results are particularly captivating when you consider how this effect could compound over multiple meals.
In this study, there was a perceived 100% difference between test meals (two eggs compared to four, 30g of cheese compared to 60g). By extension, what if the subjects thought that instead of a four-egg omelette with 60g of cheese, they were eating a six-egg omelette with 90g of cheese? Would there be an even greater decrease in energy intake at the ad libitum lunch?
Moving further down the rabbit hole, what if the researchers utilized this portion deception strategy at breakfast and lunch instead of only breakfast? Would that result in even fewer calories consumed for the rest of the day?
The obvious limitation of this trial is its short duration. The results cannot automatically be extrapolated over a longer duration. A point of diminishing returns is inevitable, and it’s possible that no further effect would be observed with this strategy over multiple meals.
Nonetheless, more trials are warranted to tease out the answers to the above questions. As widespread rates of obesity continue to climb, it’s prudent to explore innovative strategies that can have a meaningful impact.
As evidenced by the featured study, the perception that a meal is more energy dense than it actually is can elicit greater levels of satiety. To further expand on the potential of this phenomenon, let’s take a look at some other evidence that showcases the ability of a subjective mental state to influence physiology.
In one such study, the effect of perceived time passing on blood glucose levels was examined. Subjects with type 2 diabetes were randomized to one of three experimental conditions: fast, normal, and slow. In each condition, subjects played video games for 90 minutes.
In the normal group, participants viewed a clock that indicated the actual time passing while they played video games. In the slow group, participants viewed a clock rigged to run two times slower. Though the intervention was 90 minutes, subjects in this group were under the perception that only 45 minutes had passed. In the fast condition, subjects viewed a clock that ran two times faster, leading them to believe that 180 minutes had passed by the end of the task period.
It was found that participants in the fast group showed a greater decrease in blood glucose levels than those in the normal group. In contrast, participants in the slow group showed a smaller decrease in blood glucose than those in the normal group.
In addition, participants in the fast condition (i.e., those who thought 180 had elapsed) reported being hungrier at the end of the intervention period.
In another study that sought to determine whether cognition affects blood glucose levels, subjects took part in two interventions. In each intervention, they consumed a beverage containing 62g of sugar, but in condition one they believed it contained 0g of sugar and in condition two they thought it contained 124g of sugar.
Shockingly, the outcomes display that blood glucose levels increased in accordance with how much sugar participants believed they consumed rather than how much they actually consumed.
Lastly, and most similar to the main study of discussion, in this one, participants consumed the same milkshake on separate occasions, but with two different labels. In the “indulgent” condition, the shake was presented as containing 620 calories with 30g of fat. In the “sensible” condition, the shake was presented as containing 140 calories with 0g of fat.
It was observed that when subjects consumed the indulgent shake, they experienced a significantly steeper reduction in ghrelin. Physiologically, this suggests that they were more satisfied following the indulgent shake than the sensible shake, despite equal nutrition content.
Although often ignored, one’s mindset is a key component in various aspects of health. Current evidence displays a clear and strong link between the mind and body. The power of perception cannot be understated. The placebo effect is very real. We see time and time again in the research setting that ingesting a placebo can exert striking physiological outcomes.
If an individual believes the ingestion of something will exert a beneficial effect, then it most likely will. Likewise, if they believe they are about to consume something that will promote a powerful satiety effect, it may very well exert a higher degree of fullness than might be predicted based on its energy and macronutrient content.
While the available evidence in this area is compelling, more research is needed to elucidate how exactly we can practically apply this knowledge into an effective strategy to improve long-term weight loss and maintenance outcomes.