How diet influences taste sensitivity and preference

by Iqbal Pittalwala, University of California - Riverside

Credit: CC0 Public Domain

What you eat influences your taste for what you might want to eat next. So claims a University of California, Riverside, study performed on fruit flies.

26 dec 2021--The study, published in the Journal of Neuroscience, offers a better understanding of neurophysiological plasticity of the taste system in flies.

To maintain ideal health, animals require a balanced diet with optimum amounts of different nutrients. Macronutrients like carbohydrates and proteins are essential; indeed, an unbalanced intake of these nutrients can be detrimental to health. Flies require macronutrients such as sugars and amino acids for survival. They use the gustatory system, the sensory system responsible for the perception of taste, to sense these nutrients and begin feeding.

In their experiments in the lab, the researchers Anindya Ganguly and Manali Dey, led by Anupama Dahanukar, fed adult flies different diets: A balanced diet, a sugar-reduced and protein-enriched diet, and a sugar-enriched and protein-depleted diet. They ensured that all three diets were similar in total calorie content and tested the flies daily for a week to examine modifications in their food choice and taste sensitivity. 

The researchers report that diet affects dopamine and insulin signaling in the brain, which, in turn, affects the flies' peripheral sensory response, which is comprised of neurons directly involved in detecting external stimuli. This response then influences what the flies eat next.

"We found diet changed the flies' taste preference," said Dahanukar, an associate professor of molecular, cell and systems biology. "For a diet with excess protein at the expense of carbohydrates, the flies' taste sensitivity changed so that they mounted a compensatory behavioral response in the short term to eat more carbohydrates and less protein in order to regain a balanced diet."

What this may mean for other animals, including humans, is that conserved signaling pathways could play a role in mounting similar diet-induced changes in taste. Individuals on a high sugar diet could see a dampening of sugar taste, making sugars less palatable at least for the short term. Similarly, a low protein diet would enhance umami taste, increasing the value of protein-rich foods to be consumed next.

"Changes in gene expression appear to be involved," said Ganguly, a former graduate student at UC Riverside and now a postdoctoral researcher at UC Santa Barbara. "We see these changes in flies based on dietary exposure for just a day or two."

Interestingly, when the flies that were fed unbalanced diets were returned to a balanced diet, their taste sensitivity returned to baseline levels, suggesting that changes in taste preference are reversible. 

"Our work shows that imbalances in diet affect your taste preferences in a way that help you in the short term at least," said Dey, a graduate student in Dahanukar's lab. "They help you change your taste so that you prefer foods that benefit you, foods that would help you achieve metabolic homeostasis again."

Dahanukar cautioned, however, that long term effects on consumption may be more complex. For example, research by other scientists has shown that while flies raised on a high sugar diet saw their sugar response decrease in the short term, flies maintained on that diet consumed more of that food in the long term.

Dahanukar, Ganguly, and Dey were joined in the study by Christi Scott and Vi-Khoi Duong. Scott is a former graduate student and postdoctoral researcher at UCR. She helped analyze transcriptome data. Duong is a former undergraduate student who did his honors thesis in Dahanukar's lab. He is now in dental school.

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More information: Anindya Ganguly et al, Dietary Macronutrient Imbalances Lead to Compensatory Changes in Peripheral Taste via Independent Signaling Pathways, The Journal of Neuroscience (2021). DOI: 10.1523/JNEUROSCI.2154-20.2021

Provided by University of California - Riverside 

8 fresh ways fruits and vegetables are getting into your diet

Half of Americans are determined to eat more fruits and vegetables this year according to Innova Market Insights. Because fruits and vegetables are now in just about every food and beverage category, consumers shouldn't have a problem doing so.

19 oct 2015-- In the October issue of Food Technology magazine published by the Institute of Food Technologists (IFT), senior associate editor Karen Nachay looks at eight different ways fruits and vegetables are turning up in unexpected places.

1. Cauliflower: From 2013 to 2014 Innova Market Insights found a 22 percent increase in global product launches containing cauliflower. It can be roasted, mashed, pureed and included in everything from pizza to ice cream.
2. Exotic Fruits and Vegetables: Consumers are becoming more willing to try more than just apples and oranges these days and fruits and vegetables like kohlrabi, rhubarb, dragon fruit, passion fruit, sour cherry, prickly pear, and celeriac are easier to find in your local grocery store.
3. Cruciferous Vegetables: Now that consumers are realizing that these types of vegetables can taste good when properly prepared (CCD Innovation Culinary Trend Mapping Report, 2014), chefs are turning to unique preparations of parsnips, turnips, rutabagas, dinosaur kale and sea vegetables.
4. Coconut Water: New blends of coconut water with other fruit and vegetable juices highlight tropical fruits like mango and even spinach, red beet, and carrot juices.
5. Yogurt: Yogurt is taking on a savory twist with the addition of new flavors like sweet potato, beet, butternut squash, tomato, kimchi, coconut lemongrass, fig and parsnip.
6. Chilled Soups: While most people think of gazpacho as tomato-based cold soup, the addition of new fruits and vegetables like papaya, watermelon, cucumber, and lemon coriander give this classic soup a new appeal.
7. Sweet Potatoes: Sweet potatoes are no longer just ingredients in pies and side dishes; companies are using sweet potatoes as ingredients in juices, muffins, cheesecake, sauces, and even beer.
8. Natural Food Coloring: As consumers are scrutinizing food labels with synthetic ingredients, manufacturers are turning to fruits and vegetables for naturally derived coloring options. Fruits and vegetables can be minimally processed into purees or juice concentrates to extract the pigments that give them their color.

More information: Read the abstract in Food Technology here: www.ift.org/food-technology/past-issues/2015/october/columns/ingredients.aspx

Provided by Institute of Food Technologists

Diet, nutrient levels linked to cognitive ability, brain shrinkage

New research has found that elderly people with higher levels of several vitamins and omega 3 fatty acids in their blood had better performance on mental acuity tests and less of the brain shrinkage typical of Alzheimer's disease – while "junk food" diets produced just the opposite result.

29 dec 2011--The study was among the first of its type to specifically measure a wide range of blood nutrient levels instead of basing findings on less precise data such as food questionnaires, and found positive effects of high levels of vitamins B, C, D, E and the healthy oils most commonly found in fish.

The research was done by scientists from the Oregon Health and Science University in Portland, Ore., and the Linus Pauling Institute at Oregon State University. It was published today in Neurology, the medical journal of the American Academy of Neurology.

"This approach clearly shows the biological and neurological activity that's associated with actual nutrient levels, both good and bad," said Maret Traber, a principal investigator with the Linus Pauling Institute and co-author on the study.

"The vitamins and nutrients you get from eating a wide range of fruits, vegetables and fish can be measured in blood biomarkers," Traber said. "I'm a firm believer these nutrients have strong potential to protect your brain and make it work better."

The study was done with 104 people, at an average age of 87, with no special risk factors for memory or mental acuity. It tested 30 different nutrient biomarkers in their blood, and 42 participants also had MRI scans to measure their brain volume.

"These findings are based on average people eating average American diets," Traber said. "If anyone right now is considering a New Year's resolution to improve their diet, this would certainly give them another reason to eat more fruits and vegetables."

Among the findings and observations:

• The most favorable cognitive outcomes and brain size measurements were associated with two dietary patterns – high levels of marine fatty acids, and high levels of vitamins B, C, D and E.
• Consistently worse cognitive performance was associated with a higher intake of the type of trans-fats found in baked and fried foods, margarine, fast food and other less-healthy dietary choices.
• The range of demographic and lifestyle habits examined included age, gender, education, smoking, drinking, blood pressure, body mass index and many others.
• The use of blood analysis helped to eliminate issues such as people's flawed recollection of what they ate, and personal variability in nutrients absorbed.
• Much of the variation in mental performance depended on factors such as age or education, but nutrient status accounted for 17 percent of thinking and memory scores and 37 percent of the variation in brain size.
• Cognitive changes related to different diets may be due both to impacts on brain size and cardiovascular function.

The epidemiology of Alzheimer's disease has suggested a role for nutrition, the researchers said in their study, but previous research using conventional analysis, and looking in isolation at single nutrients or small groups, have been disappointing. The study of 30 different blood nutrient levels done in this research reflects a wider range of nutrients and adds specificity to the findings.

The study needs to be confirmed with further research and other variables tested, the scientists said.

Provided by Oregon State University

Moderate-protein diet may beat high-carb diet

By Amy Norton

NEW YORK , 19 mar 2009 – People lose weight when they cut calories, but a diet with some extra protein may be especially effective at trimming body fat and improving blood fats, a new study suggests.

Researchers found that over one year, a moderate-protein diet was better than a standard high-carbohydrate, low-fat diet at helping overweight adults shed body fat. What's more, it had greater benefits when it came to boosting "good" HDL cholesterol and lowering triglycerides, a type of blood fat that contributes to clogged arteries.

The findings, reported in the Journal of Nutrition, suggest that trading in some carbs for protein may do dieters good.

For the study, 130 overweight adults were randomly assigned to one of two calorie-restricted diets: the commonly recommended higher-carb diet, with about 15 percent of calories coming from protein, 55 percent from carbohydrates and 30 percent from fats; or a moderate-protein diet where 30 percent of calories came from protein -- including lean meat, low-fat dairy and nuts -- while 40 percent came from carbs, and 30 percent from fats.

All participants were given menu plans and attended weekly meetings with a dietitian to help them stick with their new lifestyle.

After one year, the average weight loss was similar in the two groups -- 23 pounds with the moderate-protein diet, versus roughly 19 pounds with the high-carb diet.

However, the moderate-protein former group lost more fat mass, and had greater improvements in both HDL and triglyceride levels.

The extra protein at each meal helps dieters preserve "metabolically active" muscle mass, explained lead researcher Dr. Donald K. Layman, of the University of Illinois in Urbana. At the same time, he told Reuters Health, the diet's lower carbohydrate content means lower levels of the blood-sugar-regulating hormone insulin.

So the diet encourages the body to shed more stored fat, according to Layman.

The greater improvement in triglycerides, he said, is largely the result of cutting carbs, which can raise triglyceride levels.

A problem with any diet is that people have to do it right to be successful. In this study, dieters in both groups got a lot of help, with planned menus and weekly educational sessions. Whether people would fare as well on their own is unclear.

"One of the problems with moderate protein diets is that people bring old diet concepts to their approach," Layman said.

For example, he said, the concept of eating "lots of small meals" throughout the day works when the diet is high-carb, low-fat because people are hungry more often -- but it's a bad idea with a moderate-protein diet.

"The important change is three consistent meals with balance of protein and carbohydrates at each meal," Layman advised.

"A higher protein diet is not more protein at dinner, but balanced protein at breakfast and lunch."

SOURCE: Journal of Nutrition, March 2009.

Is one diet as good as another? U of I study says no and tells you why

Any diet will do? Not if you want to lose fat instead of muscle. Not if you want to lower your triglyceride levels so you'll be less likely to develop diabetes and heart disease. Not if you want to avoid cravings that tempt you to cheat on your diet. And not if you want to keep the weight off long-term.

05 mar 2009--"Our latest study shows you have a better chance of achieving all these goals if you follow a diet that is moderately high in protein," said Donald Layman, a University of Illinois professor emeritus of nutrition. The research was published in the March Journal of Nutrition.

Layman's new study followed the weight-loss efforts of 130 persons at two sites, the U of I and Penn State University, during 4 months of active weight loss and 8 months of maintenance.

Two previous studies had looked at short-term weight loss; this one was designed to look at long-term effects, he said.

Although both plans were equal in calories, half the group followed a moderate-protein diet (40% carbohydrates, 30% protein, 30% fat) while the other followed a diet based on USDA's food-guide pyramid (55% carbohydrates, 15% protein, 15% fat).

"Persons in the first group ate twice the amount of protein as the second group," said Layman.

And the difference in protein made all the difference in improved body composition and body lipids, he said.

Although the amount of weight lost in both groups was similar, at 4 months participants in the protein group had lost 22 percent more body fat than members of the food-pyramid group. At 12 months, the moderate-protein dieters had lost 38 percent more body fat.

"The additional protein helped dieters preserve muscle. That's important for long-term weight loss because muscle burns calories—if you lose muscle, and you used to be able to consume 2,000 calories without gaining weight, you'll find that now you can only eat, say, 1,800 calories without weight gain," he said.

What were the effects on lipids? Although at 4 months the food-guide pyramid appeared to be more effective in lowering LDL and total cholesterol levels, at 12 months LDL levels came back up until both diets were equally effective, Layman said.

"This is the first study to show that short-term changes in LDL cholesterol are not maintained with long-term weight loss. Most scientists believe that high cholesterol is more a factor of genetics than of diet," he said.

But the moderate-protein diet had by far the bigger effect on lowering triglycerides, and that lasted as long as individuals remained on the diet, he said.

"Of the two types of lipid problems, high triglycerides pose a greater risk for heart disease. Approximately twice as many people have high triglycerides, and people with this condition are approximately four times more likely to die from heart disease," the scientist said.

To ensure compliance, participants met every week for weigh-ins and nutrition instruction. "We taught participants how to follow their diet, how to grocery shop, and how to prepare the meals. They also measured everything they ate three days a week," he said.

"Studies that report there is no difference among diets also report that subjects were not carefully following the diets," said Layman. "It's very important to realize the difference between diet compliance and diet effectiveness."

The protein diet was easier to follow and maintain long-term, with 64 percent of the moderate-protein dieters completing the study compared to 45 percent of dieters using the high-carbohydrate diet, Layman said.

"Subjects on the moderate-protein diet reported that they weren't as interested in snacks or desserts, and they didn't have food cravings. When you eat protein, you feel full longer," he said.

Average weight loss for the protein group was 23 percent higher than the food-pyramid group, with 31 percent of "completers" in the protein group losing more of than 10 percent of their initial body weight versus 21 percent of the food-pyramid group.

Foods to prevent disease?

by Christine Courcol
PARIS, 03 nov 2008– Eating tomatoes to help prevent cancer, garlic to prevent AIDS or drinking fruit juice to ward off Alzheimer's? Despite a bevy of research, the impact of food on killer diseases remains to be proved.
Scientists agree that a balanced quality diet is key to good health, and most governments in past years have urged citizens to adopt a daily diet of five portions of fruit and veg, and three each of dairy products and starch, while cutting back fats, sugar and alcohol.
Watching what you eat, experts say, does help prevent illnesses such as diabetes, hypercholesterolaemia -- which leads to cardio-vascular disease -- or osteoporosis.
But researchers are in disagreement over illnesses not directly related to nutrition, such as cancer, AIDS or neurodegenerative diseases -- though again all recommend a balanced diet.
Among the thousands of studies on hand, one European investigation concluded that eating fruit and vegetable fibre might limit the risk of colorectal cancer.
Fruit was tipped as a possible protection against cancer of the lung, and to ward off prostate cancer, the study recommended five cups a day of catechin-rich green tea -- catechins are polyphenolic antioxidant plant metabolites.
Industrial -- or processed -- fats, already known to be harmful for the cardiovascular system, could double the risk of breast cancer while soybeans reduced the risk threefold.
But soybeans, which are rich in anti-oxydants that help cells survive, could increase the risk of infertility.
Lycopene, the bright red anti-oxydant pigment found in tomatoes and other red fruits, also was found by some researchers to reduce the risk of cancer, but the US Food and Drug Administration (FDA) says there is no solid proof for the claim.
Alzheimer's on the other hand could be kept at bay by pomegranate juice, as well as the polyphenols in a glass of red wine.
But while fish are hailed for their omega-3, a family of unsaturated fatty acids, fish are also rich in mercury and toxic PCBs, or polychlorinated biphenyls.
"There are no good or bad foods," said France's Afssa food security agency.
But eating five fruit and veggies a day and little animal fat "is plain common sense", said oncologist Dominique Belpomme.
Experts at France's national food and cancer research centre, NACRe, said a varied diet of mainly fruit and vegetables with not too much alcohol would help prevent cancers of the mouth, pharynx, oesophagus, lung, stomach, pancreas, colon-rectum and bladder.
After leafing through 7,000 studies from across the globe, the World Cancer Research Fund (WCRF) recommends avoiding food and drinks high in sugar, salt or fats and low in fibres, and instead eating fruit, vegetables, wholegrain cereals and pulses.
Eating well is also key to treating HIV-positive patients as malnutrition weakens the immune system, lowering resistance to secondary effects.
But good food cannot replace antiretrovirals despite claims to the contrary by South Africa's controversial health minister -- "Dr Beetroot" -- on fighting AIDS with garlic, lemons and veggies.

Study Finds Evidence of Genetic Response to Diet

By NICHOLAS WADE
Could people one day evolve to eat rich food while remaining perfectly slim and svelte?
This may not be so wild a fantasy. It is becoming clear that the human genome does respond to changes in diet, even though it takes many generations to do so.
Researchers studying the enzyme that converts starch to simple sugars like glucose have found that people living in countries with a high-starch diet produce considerably more of the enzyme than people who eat a low-starch diet.
The reason is an evolutionary one. People in high-starch countries have many extra copies of the amylase gene which makes the starch-converting enzyme, a group led by George H. Perry of Arizona State University and Nathaniel J. Dominy of the University of California, Santa Cruz, reported yesterday in the journal Nature Genetics.
The production of the extra copies seems to have been favored by natural selection, according to a genetic test, the authors say. If so, the selective pressure could have occurred when people first started to grow cereals like wheat and barley at the beginning of the Neolithic revolution some 10,000 years ago, or even much earlier.
Paleoanthropologists have long wondered what change in the usual primate diet of fruit and nuts enabled the emerging human lineage to support a brain that eventually swelled to three times the size of chimpanzees’.
Neural tissue requires large amounts of energy, and the usual assumption is that humans began to eat meat some 2.5 million years ago when brain volume started to expand. But another possibility is that the extra nutrients came from starch.
As soon as the human lineage split from the chimp’s about five million years ago and started to live in open woodland, its diet may have expanded to include tubers, corms and the other underground structures in which plants store starch. In support of this idea, Dr. Dominy, a paleoanthropologist, said that the teeth of early humans “are not well suited for eating meat.”
Chimpanzees, whose fruit-based diet does not include much starch, have a single amylase gene. Dr. Dominy, Dr. Perry and their colleagues believe that the number of amylase genes in the human genome had started to expand by at least 200,000 years ago and perhaps much earlier, but the exact date cannot yet be determined.
Richard Wrangham, a primatologist at Harvard and an advocate of the tuber-eating thesis, said the amylase finding was a convincing insight into the different digestive physiology of people and chimps, but that the date of 200,000 years ago, derived from limited genetic information, was not old enough to give direct support to his ideas.
The amylase enzyme studied by Dr. Perry’s team exists in the saliva, where it predigests starch and lets glucose get absorbed from the mouth into bloodstream. The evolutionary advantage of this strange arrangement is not clear, but it could provide the body with energy during episodes of diarrhea, or might protect against diarrhea. Or it could just make the digestion of starch more efficient.
Whatever the exact mechanism, the extra copies of the amylase gene seem to have arisen through positive selection, the researchers said. Their conclusion is based on comparing the genomes of the Japanese and the Yakut, a Siberian people who eat mostly reindeer. Dr. Perry, a geneticist, said he could not tell whether the Japanese, who have a high-starch diet, including rice, had gained the extra copies of the gene or whether the Yakut had lost theirs.
Geneticists realized only in 2004 that having extra copies of genes was a widespread form of variation in the human genome. Many of the extra copies seem to have arisen through mistakes in the duplication process that doubles the number of chromosomes in dividing cells. The effect of these extra copies is largely unknown and the story of the amylase gene is one of the first to be understood, at least to some degree.
Dr. Perry and his team started their research by having undergraduates at Arizona State University give samples of saliva, which were analyzed for amylase. The researchers found the amount of amylase a person produced was correlated with the number of copies they possessed of the amyloid gene, which ranged from 2 to 15. The copies are arranged in the genome like a string of beads, with each gene being about 120,000 units of DNA in length.
Wondering whether the copy number varied with diet, the researchers then collected saliva and blood samples from the Yakut and other low-starch eating populations, showing that this was indeed the case.

Low GI Diets Better for Weight Loss, Lipid Profiles, Finds Cochrane Review

July 24, 2007 — A new Cochrane review of six randomized controlled trials comparing low glycemic index (GI) or glycemic load (GL) diets with other diets has found that overweight or obese people lost more weight and had more improvement in lipid profiles with the low GI eating plans. Dr Diana E Thomas (Children's Hospital at Westmead, Sydney, Australia) and colleagues publish their findings in the Cochrane Database of Systematic Reviews.
Those on the low GI diets lost an average of 2.2 pounds (1 kg) more than those given comparison diets, which included higher GI or GL diets and conventional weight loss diets. They also had significantly better decreases in total and low-density lipoprotein (LDL) cholesterol, the researchers note. And in the two trials that evaluated only obese participants, weight loss was even more apparent — the low GI dieters lost about 9.2 pounds, compared with about 2.2 pounds shed by those on the other diets.
However, the scientists caution that enduring data are still needed. "Longer trials with increased length of follow-up will determine whether the improvements reported can be maintained and incorporated into lifestyle long-term," they say.
Two experts not connected with the review expressed mixed opinions. One said this was a great review, while the other pointed out that the difference in weight loss between the low and high GI diets was rather small.
Results Applicable in Other Developed Communities
Thomas and colleagues included six trials in their review, including a total of 202 adults from Australia, France, South Africa, Denmark and the United States. The diets lasted from five weeks to six months, and none of the studies reported any adverse effects associated with consuming a low GI diet.
As well as losing more weight, those on the low GI diets also had significantly greater loss of total fat mass and decrease in body mass index (BMI) than those on the comparison diets. "The loss of 1-2 BMI units is clinically significant as is the weight loss observed with low GI diets," Thomas et al note. "Considering the brevity of the interventions, the results are notable," they add.
Improvements in blood lipids were also significant — those on the low GI diets saw a mean drop of -0.22 mmol/L in total cholesterol and -0.24 mmol/L in LDL cholesterol (both p < 0.05).
"Our systematic review may clarify issues surrounding the role of low GI or GL diets in the management of obesity and overweight," the researchers note.
They add that the degree of overweight and obesity in the populations included in these studies "was wide, suggesting that the results would be applicable in other developed communities." However, they caution that only one trial included children (n = 16), "so care would need to be taken in generalizing results in the pediatric population."
"Excellent and Fairly Comprehensive Work"
Dr Simin Liu (director of the program on genomics and nutrition, David Geffen School of Medicine, UCLA) told heartwire: "This looks like an excellent and fairly comprehensive work, which essentially confirms what we have seen in our epidemiologic work."
But another expert is not that impressed by the findings. Dr Lawrence Cheskin (Director, Johns Hopkins Weight Management Center, Baltimore, Maryland) commented to heartwire: "It strikes me that the difference in weight loss between low and high GI diets is, while statistically significant, of a rather tiny magnitude."
Cochrane Database Syst Rev. Published online July 18, 2007.