Calorie restriction, ad libitum feeding, and cancer

The inhibition of cancer by calorie restriction was discovered over 50 years ago. By 1950 it had been well characterized and there existed sufficient data to propose a mechanism of action. For reasons that remain unclear, but are probably related to the perception of the calorie restricted rodent as "small" and the ad libitum feeding regimen as more "normal," the concept of calorie restriction has been largely ignored by investigators after this time. Hence, despite the fact that calorie restriction is one of the oldest, best-documented, and most effective ways known to reduce cancer risk in rodents, it has had little impact on modern cancer research. In this report the history of calorie restriction is briefly reviewed, and a mechanism of action is proposed that involves increased production of ACTH and decreased production of gonadotrophins. It is further proposed that these changes may come about in part from the restriction of the time during which feeding is permitted as well as from the restriction of food per se. There is renewed interest in calorie restriction due in part to the growing recognition that there are differences in the efficiency of utilization of various sources of energy, in particular that fat calories are utilized more efficiently and provide more usable energy than carbohydrate calories. New data are presented indicating that the apparent enhancement by dietary fat of mammary cancer in rats is really a manifestation of the caloric effect. Further, the effect is abolished by moderate calorie restriction of only 15-20%. The application of these findings to the prevention of cancer in humans is considered.     

Chefs' Opinions About Reducing the Calorie Content of Menu Items in Restaurants

Modifying the energy content of foods, particularly foods eaten away from home, is important in addressing the obesity epidemic. Chefs in the restaurant industry are uniquely placed to influence the provision of reduced‐calorie foods, but little is known about their opinions on this issue. A survey was conducted among chefs attending US culinary meetings about strategies for creating reduced‐calorie foods and opportunities for introducing such items on restaurant menus. The 432 respondents were from a wide variety of employment positions and the majority had been in the restaurant industry for ≥20 years. Nearly all chefs (93%) thought that the calories in menu items could be reduced by 10–25% without customers noticing. To decrease the calories in two specific foods, respondents were more likely to select strategies for reducing energy density than for reducing portion size (P < 0.004). Low consumer demand was identified as the greatest barrier to including reduced‐calorie items on the menu by 38% of chefs, followed by the need for staff skills and training (24%), and high ingredient cost (18%). The majority of respondents (71%) ranked taste as the most influential factor in the success of reduced‐calorie items (P < 0.0001). The results of this survey indicate that opportunities exist for reducing the energy content of restaurant items. Ongoing collaboration is needed between chefs and public health professionals to ensure that appealing reduced‐calorie menu items are more widely available in restaurants and that research is directed toward effective ways to develop and promote these items.     

Rapid calorie metering inad lib rats

Adult wistar rats of either sex housed in individual cages and fedad lib were used to investigate the effects of calorie content and taste on ingestion. A 15 min single-choice solution (water, quinine, sucrose, saccharin) test as well as 1 h mixed diet (stock diet, sucrose-mixed, saccharin-mixed, quinine-mixed) tests were used. Calorically-rich sucrose either in solution or in mixed-diet was preferentially ingested. Tasteper se has not influenced calorie intake, as intake on sweet saccharin (3.4 ±0.4 cal) or on bitter quinine (3.3 ±0.6 cal) was similar to intake on stock diet (4.8 ±0.8 cal). Increased 5 min intake on sucrose solution (4.6 ±0.1 ml) over intake of other test solutions (saccharin 3.5 ±0.2 ml, quinine, 1.2 ±0.3 ml, water 2.1 ±0.1 ml) and calorie intake suppression on 1 h stock diet immediately following sucrose solution intake, indicate rapid calorie metering, probably based on fast-acting specific gustatory signals     

Expression of the synaptic exocytosis‐regulating molecule complexin 2 in taste buds and its participation in peripheral taste transduction

Taste information from type III taste cells to gustatory neurons is thought to be transmitted via synapses. However, the molecular mechanisms underlying taste transduction through this pathway have not been fully elucidated. In this study, to identify molecules that participate in synaptic taste transduction, we investigated whether complexins (Cplxs), which play roles in regulating membrane fusion in synaptic vesicle exocytosis, were expressed in taste bud cells. Among four Cplx isoforms, strong expression of Cplx2 mRNA was detected in type III taste cells. To investigate the function of CPLX2 in taste transduction, we observed taste responses in CPLX2‐knockout mice. When assessed with electrophysiological and behavioral assays, taste responses to some sour stimuli in CPLX2‐knockout mice were significantly lower than those in wild‐type mice. These results suggested that CPLX2 participated in synaptic taste transduction from type III taste cells to gustatory neurons.

     

Diet-Induced Obesity Reduces the Responsiveness of the Peripheral Taste Receptor Cells

Introduction

Obesity is a growing epidemic that causes many serious health related complications. While the causes of obesity are complex, there is conclusive evidence that overconsumption coupled with a sedentary lifestyle is the primary cause of this medical condition. Dietary consumption is controlled by appetite which is in turn regulated by multiple neuronal systems, including the taste system. However, the relationship between taste and obesity has not been well defined. Growing evidence suggests that taste perception in the brain is altered in obese animals and humans, however no studies have determined if there are altered taste responses in the peripheral taste receptor cells, which is the initiation site for the detection and perception of taste stimuli.

Methodology/Principal Findings

In this study, we used C57Bl/6 mice which readily become obese when placed on a high fat diet. After ten weeks on the high fat diet, we used calcium imaging to measure how taste-evoked calcium signals were affected in the obese mice. We found that significantly fewer taste receptor cells were responsive to some appetitive taste stimuli while the numbers of taste cells that were sensitive to aversive taste stimuli did not change. Properties of the taste-evoked calcium signals were also significantly altered in the obese mice. Behavioral analyses found that mice on the high fat diet had reduced ability to detect some taste stimuli compared to their littermate controls.

Conclusions/Significance

Our findings demonstrate that diet-induced obesity significantly influences peripheral taste receptor cell signals which likely leads to changes in the central taste system and may cause altered taste perception.     

Availability of and Ease of Access to Calorie Information on Restaurant Websites

Objective

Offering calories on restaurant websites might be particularly important for consumer meal planning, but the availability of and ease of accessing this information are unknown.

Methods

We assessed websites for the top 100 U.S. chain restaurants to determine the availability of and ease of access to calorie information as well as website design characteristics. We also examined potential predictors of calorie availability and ease of access.

Results

Eighty-two percent of restaurants provided calorie information on their websites; 25% presented calories on a mobile-formatted website. On average, calories could be accessed in 2.35±0.99 clicks. About half of sites (51.2%) linked to calorie information via the homepage. Fewer than half had a separate section identifying healthful options (46.3%), or utilized interactive meal planning tools (35.4%). Quick service/fast casual, larger restaurants, and those with less expensive entrées and lower revenue were more likely to make calorie information available. There were no predictors of ease of access.

Conclusion

Calorie information is both available and largely accessible on the websites of America’s leading restaurants. It is unclear whether consumer behavior is affected by the variability in the presentation of calorie information.     

Underestimating Calorie Content When Healthy Foods Are Present: An Averaging Effect or a Reference-Dependent Anchoring Effect?

Objective

Previous studies have shown that estimations of the calorie content of an unhealthy main meal food tend to be lower when the food is shown alongside a healthy item (e.g. fruit or vegetables) than when shown alone. This effect has been called the negative calorie illusion and has been attributed to averaging the unhealthy (vice) and healthy (virtue) foods leading to increased perceived healthiness and reduced calorie estimates. The current study aimed to replicate and extend these findings to test the hypothesized mediating effect of ratings of healthiness of foods on calorie estimates.

Methods

In three online studies, participants were invited to make calorie estimates of combinations of foods. Healthiness ratings of the food were also assessed.

Results

The first two studies failed to replicate the negative calorie illusion. In a final study, the use of a reference food, closely following a procedure from a previously published study, did elicit a negative calorie illusion. No evidence was found for a mediating role of healthiness estimates.

Conclusion

The negative calorie illusion appears to be a function of the contrast between a food being judged and a reference, supporting the hypothesis that the negative calorie illusion arises from the use of a reference-dependent anchoring and adjustment heuristic and not from an ‘averaging’ effect, as initially proposed. This finding is consistent with existing data on sequential calorie estimates, and highlights a significant impact of the order in which foods are viewed on how foods are evaluated.     

Identification of novel sweet protein for nutritional applications

The prevalence of obesity and diabetes has increased exponentially in recent years around the globe, especially in India. Sweet proteins have the potential to substitute the sugars, by acting as natural, good and low calorie sweeteners. They also do not trigger a demand for insulin in diabetic patients unlike sucrose. In humans, the sweet taste perception is mainly due to taste-specific G protein-coupled heterodimeric receptors T1R2-T1R3. These receptors recognize diverse natural and synthetic sweeteners such as monelin, brazzein, thaumatin, curculin, mabinlin, miraculin and pentadin. Structural modeling of new sweetener proteins will be a great leap in further advancement of knowledge and their utility as sweeteners. We have explored the fingerprints of sweetness by studying the aminoacid composition and structure properties of the above proteins. The structural analysis of monellin revealed that the individual A or B chains of monellin are not contributing to its sweetness. However, the native conformation and ionic interaction between AspB7 of monellin with active site of T1R2-T1R3 receptor, along with hydrogen bonding stability of IleB6 and IleB8 are responsible for the sweet taste. Based on structural similarity search, we found a new hypothetical protein from Shewanella loihica, which has the presence of Asp(32) with adjacent isoleucine residues. Further, we examined the lead protein by two-step docking for the study of interaction of functionally conserved residues with receptors. The identified protein showed similar ionic and hydrophobic interactions with monelin. This gives a promising opportunity to explore this protein for potential health application in the low calorie sweetener industry viz., soft drinks, snacks, food, chocolate industries etc.     

Propranolol,a β-adrenergic antagonist,attenuates the decrease in trabecular bone mass in high calorie diet fed growing mice

We investigated the effects of high calorie and low calorie diets on skeletal integrity, and whether β-adrenergic blockade (BB) attenuates bone loss induced by dietary calorie alteration. Male 6-week-old C57BL/6 mice were assigned to either an ad-lib fed control diet (CON), a high calorie diet (HIGH), or a low calorie diet (LOW) group. In each diet group, mice were treated with either vehicle (VEH) or propranolol, a β-adrenergic antagonist. Over 12-weeks, β-blockade mitigated body weight and fat mass increases induced by the high calorie diet. Femoral trabecular bone mineral density and the expression levels of osteogenic marker genes in bone marrow cells were reduced in HIGHVEH and LOWVEH mice, and BB significantly attenuated this decline only in HIGH mice. In summary, the magnitude of bone loss induced by low calorie diet was greater than that caused by high calorie diet in growing mice, and β-blockade mitigated high calorie diet-induced bone loss. [BMB Reports 2014; 47(9): 506-511]     

Effect of food deprivation on histomorphology and cholinesterase activity of taste buds in ratst

The histomorphology and cholinesterase activity of the taste buds and the gustatory nerve fibre sin well-fed, in protein and protein-calorie deficient rats have been investigated. The nerve fibre arborisation in the taste buds is predominantly nonmyelinated and shows degenerative changes ranging from initial swelling to disintegration, fragmentation and finally complete disappearance with the increasing degree and duration of food deprivation. Coincident with these changes in the nerve fibre, the taste bud also shows various stages of degeneration. By contrast, the cholinesterase activity in the gustatory papillae shows an initial increase during the first week followed by a decline in the activity during the succeeding weeks; a second peak of cholinesterase activity appears during 4–6 weeks. The cholinesterase activity is barely detectable after the 8th week. In the more severely protein calorie restricted groups, the cholinesterase changes are more pronounced and abrupt in onset and show a total disappearance by 4–5 weeks.     

Yeast as a model to understand the interaction between genotype and the response to calorie restriction

Calorie restriction is reported to enhance survival and delay the onset of age-related decline in many different species. Several proteins have been proposed to play a role in mediating the response to calorie restriction, including the target of rapamycin kinase, sirtuins, and AMP kinase. An enhanced mechanistic understanding of calorie restriction has popularized the concept of "calorie restriction mimetics", drugs that mimic the beneficial effects of caloire restriction without requiring a reduction in nutrient intake. In theory, such drugs should delay the onset and progression of multiple age-related diseases, similar to calorie restriction in mammals. Despite the potential benefits of such calorie restriction mimetics, however, relatively little is known about the interaction between genetic variation and individual response to calorie restriction. Limited evidence from model systems indicates that genotype plays a large role in determining both the magnitude and direction of effect that calorie restriction has on longevity. Here we present an overview of these data from the perspective of using yeast as a model to study aging and describe an approach we are taking to further characterize the molecular mechanisms underlying genotype-dependent responses to calorie restriction.     

Technique to Collect Fungiform (Taste) Papillae from Human Tongue

The sense of taste is critical for human life. It informs the body about the quality of food that will be potentially ingested and stimulates metabolic processes that prepare the alimentary canal for digestion. Steady progress is being made towards understanding the early biochemical and molecular events underlying taste transduction (for a review, Breslin and Spector, 2008¹). However, progress to date has largely resulted from animal models. Yet, since marked differences in receptor specificity and receptor density vary among species, human taste transduction will only be understood by using human taste tissue. Here we describe a biopsy technique to collect human fungiform papillae, visible as rounded pink anterior structures, about 0.5 mm in diameter that contain taste buds. These biopsied papillae are used for several purposes including the isolation of viable taste bud cells, in situ hybridization, immunohistochemistry and, through techniques of molecular biology, the identification of taste-specific novel proteins.Download video file.^{(56M, mov)}     

Gustatory sensation of l- and d-amino acids in humans

Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to d-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and l-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, l-serine had mainly sweet and minor umami taste, and d-serine was sweet. We further applied Stevens’ psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).     

Effect of severe calorie restriction on the lung in two strains of mice

There is a body of literature in animal models that has suggested the development of emphysema following severe calorie restriction. This has led to the notion of "nutritional emphysema" that might have relevance in COPD patients. There have been few studies, however, that have looked closely at both the mechanics and lung structure in the same animals. In the present work, we examined lung mechanics and histological changes in two strains of mice that have substantial differences in alveolar size, the C57BL/6 and C3H/HeJ strains. We quantified the dynamic elastance and resistance at 2.5 Hz, the quasistatic pressure volume curve, and the alveolar chord lengths in lungs inflated to a lung capacity at 25-30 cm H(2)O. We found that after 2 or 3 wk of calorie restriction to 1/3 their normal diet, the lungs became stiffer with increased resistance. In addition, the lung capacity was also decreased. These mechanical changes were reversed after 2 wk on a normal ad libitum diet. Histology of the postmortem fixed lungs showed no changes in the mean alveolar chord lengths with calorie restriction. Although the baseline mechanics and alveolar size were quantitatively different in the two strains, both strains showed similar qualitative changes during the starvation and refeeding periods. Thus, in two strains of mice with genetically determined differences in alveolar size, neither the mechanics nor the histology show any evidence of emphysema-like changes with this severe caloric insult.     

Stimulation of bitterness by capsaicin and menthol: differences between lingual areas innervated by the glossopharyngeal and chorda tympani nerves

Capsaicin is viewed as a purely chemesthetic stimulus that selectively stimulates the somatosensory system. Here we show that when applied to small areas of the tongue, capsaicin can produce a bitter taste as well as sensory irritation. In experiment 1, individuals were screened for the ability to perceive bitterness from capsaicin on the circumvallate papillae. Fifteen of 25 subjects who reported at least weak bitterness rated the intensity of taste, irritation and coolness produced by 100-320 microM capsaicin and 100-320 mM menthol applied via cotton swabs to the tip (fungiform region), the posterior edge (foliate region), and the dorsal posterior surface (circumvallate region) of the tongue. Sucrose, citric acid, sodium chloride and quinine hydrochloride were applied to the same areas to assess tastes responsiveness. On average, capsaicin and menthol produced "moderate" bitterness (and no other significant taste qualities) in the circumvallate region, and weaker bitterness on the side and tip of the tongue. Sensory irritation from capsaicin was rated significantly higher at the tongue tip, whereas menthol coolness was rated higher in the circumvallate region. In experiment 2 we applied sucrose and quinine hydrochloride together with capsaicin to investigate the effects other taste stimuli might have on capsaicin's reported bitterness. As expected, adding quinine produced stronger bitterness in the circumvallate and fungiform regions, and adding sucrose significantly reduced the bitterness of capsaicin in the circumvallate region. Overall, the results suggest that capsaicin and menthol are capable of stimulating a subset of taste neurons that respond to bitter substances, perhaps via receptor-gated ion channels like those recently found in capsaicin- and menthol-sensitive trigeminal ganglion neurons, and that the glossopharyngeal nerve may contain more such neurons than the chorda tympani nerve. That some people fail to perceive bitterness from capsaicin further implies that the incidence of capsaicin-sensitive taste neurons varies across people as well as between gustatory nerves.     

Bulky high-mannose-type N-glycan blocks the taste-modifying activity of miraculin

Background

Miraculin (MCL) is a taste-modifying protein that converts sourness into sweetness. The molecular mechanism underlying the taste-modifying action of MCL is unknown.

Methods

Here, a yeast expression system for MCL was constructed to accelerate analysis of its structure–function relationships. The Saccharomyces cerevisiae expression system has advantages as a high-throughput analysis system, but compared to other hosts it is characterized by a relatively low level of recombinant protein expression. To alleviate this weakness, in this study we optimized the codon usage and signal-sequence as the first step. Recombinant MCL (rMCL) was expressed and purified, and the sensory taste was analyzed.

Results

As a result, a 2 mg/l yield of rMCL was successfully obtained. Although sensory taste evaluation showed that rMCL was flat in taste under all the pH conditions employed, taste-modifying activity similar to that of native MCL was recovered after deglycosylation. Mutagenetic analysis revealed that the N-glycan attached to Asn42 was bulky in rMCL.

Conclusions

The high-mannose-type N-glycan attached in yeast blocks the taste-modifying activity of rMCL.

General significance

The bulky N-glycan attached to Asn42 may cause steric hindrance in the interaction between active residues and the sweet taste receptor hT1R2/hT1R3.     

Gustatory intensity discrimination in rat NTS: a tool for the evaluation of neural coding theories

Summary The neural coding of taste quality in vertebrates currently is addressed by the labeledline and the across-fiber pattern theory. Experimental tests that have tried to distinguish between these theories by manipulating taste quality have been problematic in that both are fairly successful. However, the two theories maintain that different numbers of neurons participate in coding the presence of a substance. In the labeled-line theory, only those neurons labeled by that substance are supposed to be involved, whereas in the across-fiber pattern theory, all neurons responding to the substance are taken into account. We therefore expected that the theories might predict different intensity discriminating abilities among the four classical taste stimuli, which could provide a less equivocal test between the theories.A previous paper (Maes 1984) described a model for the neural basis of intensity discrimination, based on signal-detection theory. In the present paper, experimental data obtained from single neurons in the nucleus of the solitary tract of rat are analyzed in terms of this model. Whole-mouth stimulation with the four classical taste substances was used. For both theories, predictions of the intensity discriminating acuity for the four substances were derived, using different response analysis intervals, and including two plausible non-linearities in neural processing.The acuity profile across the four stimuli (consisting of the reciprocals of the four differential thresholds) turned out to be sensitive to the choice of coding theory and non-linearity. The interval chosen for response analysis had a strong effect. The predicted profiles should be checked against behavioral data on intensity discrimination in rat, but since such data are not yet available, a comparison was made with human psychophysical data, for illustrative purposes. It appeared that a unique combination of variables (tonic part of the response, across-fiber pattern coding with a contrast enhancement type of non-linearity) could be selected to match the psychophysical profile.In the Discussion, special attention is paid to the fundamental differences between the two coding theories, to the relevance of whole-mouth stimulation, and to the informational significance of various parts of the phasic/tonic response.Abbreviations AFP across-fiber pattern - CT chorda tympani - DA discrimination acuity - DT differential threshold - H sour - LL labeled line - N salty - NTS nucleus tractus solitarius - PTA pontine taste area - Q bitter - S sweet     

Techniques for universal evaluation of astringency of green tea infusion by the use of a taste sensor system

A practical method for universal evaluation of the astringency of green tea infusion by a taste sensor system was established. The use of EGCg aqueous solution as a standard enabled analysis with high accuracy and reproducibility. The sensor output was converted into taste-intensity on the basis of Weber's and Weber-Fechner laws, which was named the "EIT(ast)" value ("EIT" and "ast" are abbreviations for "Estimated Intensity of Taste" and "astringency" respectively). It was clarified that green tea infusion is to be classified into eight grades on the EIT(ast) scale. Furthermore, the high correlation of the EIT(ast) value with the human gustatory sense and the high stability of the taste sensor were proved.