In medical school I learnt that we have four senses of taste: sweet, sour, salty, and bitter.

Several years ago a fifth sense, umami, was officially added to this list. Umami is stimulated by glutamate (as in MSG) and apparently allows us to taste protein (as in meat, sea food, or cheese).

Now, Jessica Stewart and colleagues from Deakin University in Australia show that a sixth sense, i.e. the ability to orally “sense” the fat content of foods may explain differences in fat preferences (British Journal of Nutrition).

Indeed, previous studies in animals have suggested that oral hypersensitivity to fatty acids (the building blocks of fat) are associated with decreased fat intake and body weight.

In the current study, the investigators first examined the taste thresholds for different types of fatty acids (olate, linolate, and laurate) in 31 normal weight subjects and classified them as hypo- or hypersensitive. Subjects also completed a fat ranking task using custard containing varying amounts (0, 2, 6 and 10 %) of fat.

Hypersensitive subjects reported lower energy and fat intakes, had an increased ability to rank the custards based on fat content and also had a lower BMI levels.

These data suggest that the increased ability to detect nutritional fat may result in lower energy and fat intake, which in turn may result in lower body weights.

Obviously, the idea here is that people who are less sensitive to fat are likely to need more fat in their foods to get that same level of enjoyment as people with more sensitive fat receptors. Because of fat’s high caloric content, this means that they may in the end also end up with more calories, and thus, weight gain.

I can think of a number of interesting questions that these findings may prompt:

1) Is the increased ability to taste fat genetic or are changes in fat-sensitivity determined by habitual fat intake (gustatory plasticity)?

2) Does weight loss affect people’s ability to taste fat (resulting in them searching out fattier foods when on a diet)?

3) Does going on a low fat-diet increase fat sensitivity thereby allowing people to get the same pleasure out of low-fat foods?

4) Can we develop artificial compounds that can stimulate the fat receptors thereby mimicking a higher fat content of foods (like we do with artificial sweeteners)?

Lots of interesting questions, which may not only explain why some people derive more pleasure from fatty foods than others but also open new possibilities for the food industry to manipulate the taste of foods (hopefully to our benefit).

I’d love to hear from my readers regarding their thoughts on “tasting” fat.

AMS
Edmonton, Alberta

Reader of these pages are by now probably quite familiar with the complexity of ingestive behaviour and the importance of understanding brain function in relationship to food intake.

A study, published in this month’s issue of Obesity, illustrates how differences in brain function between obese and non-obese people can explain important differences in response to food.

In this study, Laura Martin and colleagues from the Kansas Medical Center, used functional magnetic resonance imaging (fMRI) to examine changes in brain activity in obese and normal weight adults while they viewed food and nonfood images in premeal and postmeal states.

Both in the premeal and postmeal state, obese participants showed showed increased activation in the anterior cingulate cortex (ACC) and the medial prefrontal cortex (MPFC), regions of the brain responsible for the reward response and impulsiveness, respectively.

In addition, activation of the ACC was associated with decreased levels of self-reported disinhibition while MPFC activation was associated with increased self-reported hunger amongst obese participants.

These findings clearly suggest that brain function associated with food motivation differs in obese and non-obese adults and may well explain the different susceptibilities to weight gain and variability in response to diet interventions.

Given the emerging science on brain plasticity, it is certainly of interest whether or not these differences in brain function are acquired or are indeed innate. Whatever the case, we need to understand and acknowledge that our brains respond differently to the same food stimuli which easily explains why some people may find it much harder to resist overeating in our current obesogenic environment than others.

As I have said before, the obesity epidemic is simply the natural response to our unnatural environment.

AMS
Edmonton, Alberta

Regular readers will recall previous posts on the important influence of social networks on behaviours and risk of weight gain.

Now a study by Sarah-Jeanne Salvy and colleagues from the State University of New York at Buffalo, NY, published in the Annals of Behavioral Medicine, examines whether social activities can potentially affect eating behaviours in kids.

Fifty-four (24 males and 30 females) overweight and non-overweight youth aged 9 to 11 years old were tested using a behavioral choice paradigm which involved participants coming to the laboratory for one session to work on a computer game in pairs, either together with a friend or together with a kid that they did not know. In the game, the kids could earn points exchangeable either for food or for free-play time - as a result of the study design, the play time would either be with their friend or with the unfamiliar kid.

For half of the sample, during the game, the cost of food points increased, while the cost of time playing with another child remained constant. For the other half of the sample, the cost of points for social play increased, while the cost of food points remained constant.

When matched with an unfamiliar kid, the participants substituted food for social activities when the cost of social time with an increased and substituted food for social activities when the cost of food increased - in other words, the kids chose whatever was easier to get.

In contrast, when interacting with a friend, participants did not substitute food for social interactions irrespective of wether or not the choices became easier or difficult.

The results of this experiment clearly support the notion that social interactions may play a key role in food choices and that social interactions with a friend can well serve as a substitute for food in both lean and overweight youth.

Importantly, I would imagine that the reverse also holds true: i.e. kids who don’t get enough time to spend with their friends can substitute this friendship with food. The key word here is probably “friends” as it is apparently not enough to just spend time with any old kid - it’s got to be a friend to be valued as much as food.

So could the fact that our kids don’t get enough time to hang out with their friends be an important driver of the childhood obesity epidemic?

I certainly welcome views on this from my readers!

AMS
Edmonton

Taking enough time to eat has long been advocated as an effective weight management strategy (remember, the real problem with fastfood is more often the “fast” than the “food”). I have also previously blogged about how eating too fast is an important predictor of obesity.

Not surprisingly therefore, various strategies to slow down eating are being explored to help manage weight (one such approach is the SMART system, an oral device that reduces bite size, thereby significantly increasing meal times).

Another novel approach to reducing “tachyphagia” was now explored in kids using a talking scale called a “Mandometer“. According to the manufacturer’s website, the device, originally intended for the treatment of eating disorders, “ allows the patient to see a rate of eating displayed on the screen that describes the rate at which normal individuals eat that amount of food and feel satiety as they eat. At the same time, the patient’s own eating speed and perception of satiety is shown on the screen.” 

In this study, by Ford and colleagues from the University of Bristol, UK, published in the latest issue of the British Medical Journal, 106 kids (aged 9-17) were radomised to either using the Mandometer, which provided real time feedback during meals to slow down versus standard lifestyle modification.

Participants using the Mandometer were initially trained once a week for six weeks, every second week for a further six weeks, and once every sixth week thereafter. The research nurse telephoned the patients to offer support and encouragement every second week from week 12 onwards.

Over the 18 month duration of the study, participants using the Mandometer had significantly lower BMI levels and a significant reduction in meal size.

The authors conclude that retraining eating behaviour with a feedback device is a useful adjunct to standard lifestyle modification in treating obesity among adolescents.

AMS
Edmonton, Alberta

An important aspect of enjoying food, in addition to the actual taste and mouth feel, is the complex sensory stimulation of the olfaction system. After the food enters the oral cavity, aroma molecules find their way to the sensitive olfactory nerve endings in the nose by making their way up the back of the throat into the nasal cavity (apparently the nose has a clever way of telling whether this aroma is coming from the food on your plate or from the food in your mouth).

This activation of specific brain areas by a retronasally sensed food odor is not only associated with the perception of the aroma of the food that is consumed but is also hypothesized to directly contribute to its satiating effect (sensory-related satiation).

A paper by Rianne Ruijschop and colleagues from The Netherlands, published in the Journal of Agricultural and Food Chemistry, provides a splendid overview of this fascinating area of research.

In this paper, Ruijschop and colleagues describe a series of experiments that examine a wide range of factors that can affect retronasal olfaction-related satiation.

Not surprisingly, solid and semisolid foods that required a greater amount of chewing and swallowing elicited a stronger and longer-lasting retronasal aroma release pattern than the rather short-lived spiked pattern observed with liquid foods. A higher extent of retronasal aroma release may therefore be one of the explanations why solid foods appear to be more satiating than liquid foods.

Indeed, the researchers did observe a negative trend between the extent of retronasal aroma release and the amount of ad libitum food intake. Subjects who had a higher extent of retronasal aroma release tended to consume less.

However, retronasal aroma release intensity and profile morphology appeared to be subject specific, which may support the hypothesis that subject differences in the extent of retronasal aroma release are linked to subject differences in sensory satiation and food intake behavior.

In further studies, the researchers found that certain aromas were better at eliciting a satiation response than others. Thus, aromas that suggest fat content (i.e., lactones) were less effective in creating a satiation response than aromas suggesting carbohydrate content (i.e., maltol) or the breakdown of protein (i.e., “animalic”). In a separate experiment, custard products with the addition of maltol or animalic at sensory detection threshold were able to increase subjects’ feeling of fullness significantly.

These results are in line with the observation that macronutrients have different satiating efficiencies, in which protein is more satiating, followed by carbohydrate and fat as least satiating.

Based on these studies, the authors suggest that these findings may provide the rational for developing strategies for prolonging the duration of retronasal aroma release during food consumption.

Examples could include food products with an increase of aftertaste or an increased or lingering aroma release via flavor delivery systems or encapsulation technology or the development of long-chewable food structures in beverages that evoke substantially more oral processing and an increase in transit time in the oral cavity.

Furthermore, a reduction in bite size by tailored packaging may support the “right” oral processing behavior in food products. Interestingly, as blogged previously, eating too fast has been previously associated with increased risk for obesity.

Differences in the extent of retronasal aroma release during consumption may be one of the reasons that people vary in their satiation characteristics, which may prevent them from overeating or not. Whether or not there is a difference in this effect between normal weight and obese people is not known.

As the authors point out, integration of these findings into novel food products may provide a new way to reduce food consumption.

While we wait for these new foods here are my retronasal olfaction-based satiation tips:

1) Take small bites
2) Chew your food thoroughly
3) Don’t drink your calories

Remember, the main problem with fast food is not the “food” - it’s the “fast”.

Happy Holidays,

AMS

p.s. As I am planning to take it easy for the next couple of days you are likely to see sporadic posts till the new year.