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 and 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. Some primary strategies to manage appetite include increasing protein and fiber intake. There are other nuances that may prove useful as well, such as pre-meal water consumption and altering expectations.
In reference to the latter, as portion sizes inevitably decrease during a phase of weight loss, an individual might look at a plate of food and conclude that it will have little effect on their raging appetite before they even take a bite of it.
If we can alter this person’s expectations, and make them believe that their impending meal will generate a high level of satiety, this could bolster dietary success by decreasing energy intake at subsequent meals and/or preventing snacking between meals.
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 (subjects completed both interventions). Subjects visited the testing facility on two separate occasions one week apart.
In each arm of the trial, participants consumed a breakfast test meal of an egg and cheese omelet containing three medium eggs and 45 grams (g) of cheese.
In the “small” condition, subjects were under the guise that they were receiving a two-egg omelet with 30g of cheese. In the “large” condition, they thought the omelet was made with four eggs and 60g of cheese. Again, in reality, the omelet 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 omelet, imagine eating the whole thing, and then think about how long they would expect it to stave off hunger.
Following the consumption of the omelet, 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 omelet with 60g of cheese (“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.
There were no significant differences in total ghrelin response between interventions.
In regard to overall energy intake, when subjects thought they consumed a large omelet, 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 omelet rather than a small omelet.
These results are particularly captivating when you consider how this effect could compound over multiple meals.
In this specific study, there was a perceived 100% difference between test meals (two eggs compared to four, 30g of cheese compared to 60g). It makes you wonder, what if the subjects thought that instead of a four-egg omelet with 60g of cheese, they were eating a six-egg omelet with 90g of cheese? Would we see a greater decrease in energy intake at the ad libitum lunch? A greater decrease in total daily energy intake?
Going 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. You cannot expect that these positive findings would increase in a similar magnitude over a longer period of time or across more meals. Nonetheless, this is a fascinating area and I would love to see more trials done to tease out the answers to some of these questions.
As evidenced by the aforementioned trial, if you think the food you are about to consume is more energy-dense than it actually is, you will expect a greater satiating effect, and consequently, are more likely to consume smaller portions of food at subsequent meals. Other research has also demonstrated the ability of subjective mental states to influence human physiology.
In this 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.
At the end of the trial, 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 lesser decrease in blood glucose than those in the normal group.
In addition, participants in the fast condition (i.e. who thought more time 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. 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.
It was found that blood glucose levels increased in accordance with how much sugar participants believed they consumed rather than how much they actually consumed.
Lastly, similar to the foremost study we examined, 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.
The results displayed that when subjects consumed the indulgent shake, they experienced a significantly steeper reduction in ghrelin. Physiologically speaking, this suggests that they were more satisfied following the indulgent shake than the sensible shake, despite equal nutrition content.
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 you think you are ingesting something that will exert a beneficial effect, then it most likely will.
Although often ignored, one’s mindset is a key component in various aspects of health. In aggregate, the above research displays a clear and strong link between the mind and body; expectations affect hunger and satiety, which can impact total daily energy intake, and ultimately, dietary success.
While this data is compelling, more research in this area 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.