http://scholar.google.com/scholar?q=effect+of+diet+on+perception+of+time

http://www.psychosomaticmedicine.org/cgi/reprint/35/2/104.pdf

Francois and Hoagland have suggested that body rhythms are regulated by an internal chemical clock which is bsensitive to variations in metabolism. An increased metabolic rate acts to speed up internal time whereas a decreased metabolic rate produces the opposite effect. A speeding or a slowing down of the internal clock can be inferred from overestimation or underestimation of the duration of standard stimuli. Subjects with hyperthyroidism or an increased internal body temperature overestimate the duration of short auditory stimuli, while subjects suffering from depressive episodes or taking barbiturates underestimate the duration. Changes in mood have also been correlated with changes in time sense in acute psychiatric patients. Greater anxiety was associated with faster internal time.

http://www.primidi.com/2005/02/21.html#a1118

In “Life on the Scales,” Science News recently wrote that some simple mathematical equations, known as quarter-power scaling laws, can explain the metabolic rates of living organisms. For example, “an animal’s metabolic rate appears to be proportional to mass to the 3/4 power.” And this “3/4-power law appears to hold sway from microbes to whales, creatures of sizes ranging over a mind-boggling 21 orders of magnitude.” The ecologists, physicists and chemists behind this research are now successfully applying this equation to plants, fish, full ecosystems and even biology and genetics, by adding a new key parameter: temperature. Please read this fascinating article for many more details and references. But save some time to read another long article, “Ecology’s Big, Hot Idea,” published by PLoS Biology, which states that “the way life uses energy is a unifying principle for ecology in the same way that genetics underpins evolutionary biology.” Read more…

The Science News article starts with a simple observation. Although a mouse has a shorter life than an elephant, both clock approximately the same number of heartbeats during their lives.

The article being referred to:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=535575

“We’ve found that despite the incredible diversity of life, from a tomato plant to an amoeba to a salmon, once you correct for size and temperature, many of these rates and times are remarkably similar,” says Gillooly.

“Metabolic rate is, in our view, the fundamental biological rate,” Gillooly says. There is a universal biological clock, he says, “but it ticks in units of energy, not units of time.”

http://www.bc.edu/bc_org/rvp/pubaf/chronicle/v5/Mr27/barry.html

Fast food offers an obvious but appropriate symbol for US popular culture, says Assoc. Prof. Ann Marie Barry (Communication): quick to obtain, easy to digest - and of little nutritional value.

But the metaphor goes deeper, Barry explains. Most fast-food restaurants utilize red and yellow in their design because of their subtle effect on human senses, she said, including an exaggerated perception of time. Customers who feel they have spent a long, leisurely meal actually replace one another in fairly rapid succession, thus enabling the restaurant to do a high volume of business.

THIS ARTICLE IS OUTSTANDING:

http://www.sciencenews.org/articles/20050212/bob9.asp

For most of the past 70 years, ecologists had no explanation for the 3/4 exponent. “One colleague told me in the early ‘90s that he took 3/4-scaling as ‘given by God,’” Brown recalls.

The beginnings of an explanation came in 1997, when Brown, West, and Enquist described metabolic scaling in mammals and birds in terms of the geometry of their circulatory systems. It turns out, West says, that Rubner was on the right track in comparing surface area with volume, but that an animal’s metabolic rate is determined not by how efficiently it dissipates heat through its skin but by how efficiently it delivers fuel to its cells.

Rubner should have considered an animal’s “effective surface area,” which consists of all the inner surfaces across which energy and nutrients pass from blood vessels to cells, says West. These surfaces fill the animal’s entire body, like linens stuffed into a laundry machine.

The idea, West says, is that a space-filling surface scales as if it were a volume, not an area.  Thus, an animal’s effective surface area scales as if it were a three-dimensional, not a two-dimensional, structure.

This creates a challenge for the network of blood vessels that must supply all these surfaces. In general, a network has one more dimension than the surfaces it supplies, since the network’s tubes add one linear dimension. But an animal’s circulatory system isn’t four dimensional, so its supply can’t keep up with the effective surfaces’ demands. Consequently, the animal has to compensate by scaling back its metabolism according to a 3/4 exponent.

Though the original 1997 model applied only to mammals and birds, researchers have refined it to encompass plants, crustaceans, fish, and other organisms. The key to analyzing many of these organisms was to add a new parameter: temperature.

Mammals and birds maintain body temperatures between about 36°C and 40°C, regardless of their environment. By contrast, creatures such as fish, which align their body temperatures with those of their environments, are often considerably colder. Temperature has a direct effect on metabolism—the hotter a cell, the faster its chemical reactions run.

In 2001, after James Gillooly, a specialist in body temperature, joined Brown at the University of New Mexico, the researchers and their collaborators presented their master equation, which incorporates the effects of size and temperature. An organism’s metabolism, they proposed, is proportional to its mass to the 3/4 power times a function in which body temperature appears in the exponent. The team found that its equation accurately predicted the metabolic rates of more than 250 species of microbes, plants, and animals. These species inhabit many different habitats, including marine, freshwater, temperate, and tropical ecosystems.

The equation gave the researchers a way to compare organisms with different body temperatures—a person and a crab, or a lizard and a sycamore tree— and thereby enabled the team not just to confirm previously known scaling laws but also to discover new ones. For instance, in 2002, Gillooly and his colleagues found that hatching times for eggs in birds, fish, amphibians, and plankton follow a scaling law with a 1/4 exponent.

When the researchers filter out the effects of body temperature, most species adhere closely to quarter-power laws for a wide range of properties, including not only life span but also population growth rates. The team is now applying its master equation to more life processes—such as cancer growth rates and the amount of time animals sleep.

http://scienceblogs.com/neurophilosophy/2007/09/diet_brain_evolution.php

Diet & brain evolution: another item on the menu

At some point in the distant past, there was a dramatic increase in brain size in our hominid ancestors. From approximately 2 million years ago, to the present day, there has been an increase of more than 300% in brain volume in the hominid lineage: the brain of Homo erectus had a volume of about 400 milliliters, while that of modern humans is roughly 1,400 ml.

The size of the human brain cannot be accounted for merely by an increase in body size, because Homo erectus was similar in size to modern humans, so the driving for this increase in brain size (or “encephalization") is still a topic of debate among anthropologists, evolutionary biologists and neuroscientists.

Traditionally, it was believed that our ancestors evolved a large brain to accomodate language and tool use. But in recent years, a number of theories have focused on the role of diet in human brain evolution. During the course of human evolution, changes in diet were brought about by the control of fire, the domestication of plants and animals, and the development and mastery of stone tool technology.

According to one theory, increased consumption of meat by our ancestors provided the additional energy needed for brain expansion. (Cooking would have further increased the amount of calories obtained from meat.) Another holds that a switch to a seafood-rich diet would have provided polyunsaturated fatty acids which, when incorporated into nerve cell membranes, would have made the brain function more efficiently.

And now, a study published in Nature Genetics adds starchy tubers to the smorgasbord of foodstuffs that may have contributed to the expansion of the human brain.

The brain of modern humans is an energy-hungry organ. At rest, it consumes about one quarter of the body’s energy, despite comprising only 2% of the total body mass. (In comparison, the brains of apes about 8% of the body’s energy.) However, the calorific intake of humans is similar to that of other similar-sized mammals with smaller brains.

Hence, large amounts of additional energy were required for the brain expansion that occurred in the hominid lineage. One explanation for how this energy was supplied is that we traded brains for guts during our evolution: a change in diet, presumed to consist of more meat, meant that more calories could be absorbed with less effort, so that the gastrointestinal tract could shrink, thus freeing up energy that could be consumed by neural tissue. 

In the new study, which was led by George Perry of Arizona State University and Nathaniel Dominy of the University of California, Santa Cruz, a human gene called AMY1 was investigated. This gene encodes an enzyme called salivary amylase, which breaks down starch into glucose, which is the only energy source for nerve cells.

The AMY1 gene is unusual, in that the number of copies varies quite widely between populations. The researchers therefore determined the number of copies of AMY1 in populations with a high-starch diet, and compared it to the copy number in populations with a low-starch diet.

First, the genomes of 50 American students of European descent were analyzed. It was found that the number of copies of AMY1 varied from between 2 and 15, and that individuals with more copies of the gene had higher levels of the salivary amylase protein in their saliva. On the other hand, chimpanzees, which have a low-starch diet, were found to have just 2 copies of the gene, and low levels of salivary amylase.

The gene copy number in populations with high-starch diets (European Americans, Japanese, and Hadza hunter-gatherers of Tanzania) was then compared to that of populations with a low-starch diet (the Datog peoples of Tanzania, the Yakut of Russia, and the Biaka and Mbuti, both of which are rainforest hunter-gatherers from, respectively, the southern region of the Central African Republic and the Ituri forest in Zaire).

It was found that individuals from populations with a high-starch diet had, on average, more copies of the AMY1 gene than individuals from populations with a low-starch diet - twice as many of the former than the latter had 6 or more copies.

These results show that populations that have a starch-rich diet carry more copies of the AMY1 gene. The authors believe that they have provided one of the very first examples in the human genome of selective pressure resulting in changes in the number of copies of a gene.

The link between diet and brain evolution is, however, indirect. The implication of the findings is that an increase in the AMY1 copy number in our ancestors enabled them to digest starch more efficiently, providing the energy needed for expansion of the brain. It is, however, impossible to conclude that adopting a starch-rich diet was such an important event in human evolution.