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Big Brained Animals Are Sicker

Humans and other big brained animals are inherently more susceptible to disease and additional illnesses than are other species.

An evolutionary tradeoff exists between brain size and immunity, according to new research.

Bigger brained animals may be more vulnerable to a barrage of illnesses than species whose evolution has selected for immunity over braininess.

"Organisms have to deal with the limited energy they have available -- they cannot have it all," Alexander Kotrschal of Stockholm University's Department of Biology told Discovery News. Kotrschal and colleagues Niclas Kolm and Dustin Penn conducted the research, which is published in the journal Proceedings of the Royal Society B.

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Kotrschal explained that "investing more in one costly organ, such as the brain, will deduct energy away from other costly organs, like gut, muscle and fat. Humans have quite small guts compared to other primates. In fact, across primates: the larger the brain, the smaller the gut."

The researchers decided to investigate whether larger brains also could lead to reduced immune responses. They decided upon guppies as a model animal, since these little fish have a fast average time between two generations and have been well studied. Guppies also share many critical molecular pathways with humans, other mammals and numerous additional animals.

The scientists examined the relationship between brain size and immune response to scale tissue grafting in lab-grown Trinidadian guppies that were artificially selected for large or small relative brain size.

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As predicted, the smaller-brained individuals of both sexes mounted a much stronger immune response than did those with bigger brains. Having a big brain was not all bad, though. Earlier research found that female guppies with more brainpower had a cognitive advantage over others.

Kotrschal explained: "They were better at learning a numerical learning task than small-brained females."

As the studies indicate, brain size can differ not only among species, but also among individuals of the same species. Relative brain size, or how the brain measures when compared to the rest of the entire body, is the most important factor -- including very tiny creatures, such as ants and honeybees, which are considered to be quite brainy and intelligent.

"In primates, males and females generally have similar brain sizes when controlled for body size," Kotrschal said. "This is also true for humans."

On the other hand, he added that there are a few animals, such as sticklebacks (another type of fish) where one sex always seems to have a larger brain. In the case of sticklebacks, males are nearly always brainier than females. Researchers think that is because these fish must work overtime caring for, and protecting, their young.

As for when the tradeoff between brain size and immunity or other traits happens, Kotrschal believes it occurs during the very earliest stages of development.

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"For instance, (it may happen) when the embryo ‘decides' how many stem cells are attributed to neural development versus the immune system," he said.

Hans Hofmann is a professor of integrative biology at the University of Texas at Austin, where he's the director of the Center for Computational Biology and Bioinformatics.

Hofmann said it would be important to repeat the experiments in order to better determine how the tradeoff affects both innate and acquired immune function.

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"It is also interesting to ask what the underlying mechanisms are that give rise to this apparent tradeoff," he said.

It should also be noted that intelligence can help an individual to prevent some illneses, so there is a connection between brainpower and health. Two other studies published this week in the journal Biology Letters focus on how ants, honeybees and other very social insects prevent illness while living in some of the most crowded conditions imaginable.

Such insects have an arsenal of prevention techniques that include personal fastidiousness, cleaning others and reducing their contact with contagious individuals. Ants have zero tolerance for a sick ant that shows up to work. If efforts to disinfect or otherwise cure the ill ant fail, healthy ants will throw the sick individual out of the nest.

"A characteristic of the American dietary that has persisted throughout years has been its abundance." This sentence is no less true today than when it was

published in the American Journal of Clinical Nutrition in 1959

. That abundance, however, comes with a cost: Americans eat too much. That excess consumption and often poor nutrition has brought with it a multitude of life-changing and often life-threatening diseases and conditions, including obesity, diabetes, heart disease, cancer and more. Although the number of Americans who are overweight or obese has been on a steady climb since the middle of the 20th century,

a recent report by the New York Times suggests

that efforts to abate this health crisis might be gaining ground thanks to a shift in public attitudes. For the first time since the federal government began tracking dietary intake over more than four decades of data collecting, the daily calorie intake of the average American showed a sustained decline. Read on to see how the American diet has changed since the middle of the 20th century.

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While calorie counts have been on the downswing, calorie intake is still far above where it once stood. Americans' daily average caloric intake is over 500 calories higher than it was in 1970, when the average hovered around 2,169 calories per day. What does a more than 20 percent increase in caloric intake mean for the average American? Consider that a pound a fat contains 3,500 calories. Assuming that even a quarter of those calories represent excess energy beyond what's needed for daily maintenance levels, that translates into a pound of stored fat gained every month, or 12 additional pounds per year. Portion sizes have seen a similar increase over time.

According to the U.S. Department of Health & Human Services

, in the last two decades alone, food portions in American restaurants have doubled or in some cases tripled. Portion sizes began increasing in the 1970s and rose sharply in the 1980s. Many food portions greatly exceed USDA and FDA standard servings,

according to a study published in the American Journal of Public Health

. "The largest excess over USDA standards (700 percent) occurred in the cookie category, but cooked pasta, muffins, steaks and bagels exceeded USDA standards by 480 percent, 333 percent, 224 percent and 195 percent, respectively," the study found.

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According to the U.S. Department of Agriculture (PDF)

, between the 1950s and 2000, Americans consumed on average 39 percent more refined sugars. Consumption of corn sweeteners, with high-fructose corn syrup leading the charge, octupled. On average, Americans consume an estimated 156 pounds -- yes, pounds -- of added sugar per capita every year. Excessive sugar intake can lead to all kinds of negative health outcomes, including but not limited to dental problems, obesity, diabetes, liver failure and more. These concerns are what led the

Food and Drug Administration (FDA) recently to propose

a change in food labeling that would recommend the daily intake of calories from added sugars not exceed 10 percent of total consumption. More than 70 percent of U.S. adults get over 10 percent of their daily calories from sugar.

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Americans aren't just eating more sugars than they used to; we're also drinking more.

According to the Harvard School of Public Health

, before the 1950s, the standard soft drink size was 6.5 ounces. That decade, manufacturers started selling larger sizes, and by 1960 the 12-ounce can was everywhere. Fast forward 30 years, and 20-ounce bottles are ubiquitous. Today, single-use soft drinks can reach up to 64 ounces and have up to 700 calories. Since the 1970s, sugary drinks have grown from 4 percent of Americans' daily calorie intake to 9 percent. A quarter of Americans get at least 200 calories a day from soft drinks. Teens and children are particularly high consumers, too. Sugar drinks are the top calorie source for teenagers, and are consumed daily by an estimated 91 percent of children.

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Beginning in 1980, when USDA issued the first federal dietary guidelines implicating fats and cholesterol as a major source of Americans' health woes, particularly heart disease, the food industry began shifting formulas in their products that moved away from saturated fat and toward vegetable oils and carbohydrates. Low-fat diets became all the rage, with a bevy of product lines offering low-fat alternatives. What happened after Americans got turned on to low-fat foods? They got even fatter and less healthy. Foods may not have had as much saturated fat, but they made that up with an increase in sugar and refined grains, which kept calorie counts the same. The switch to hydrogenated vegetable oils and margarines also only increased health risks. Heart disease is still the number one killer in the United States, and we also have rising numbers of diabetes and obesity to contend with. In fact, despite numerous studies since the 1990s showing that low fat diets are ineffective at best and harmful at worst, the government continues to recommend a low fat diet.

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Go to the snack aisle of any supermarket or convenience store in the United States, and you'll find a wide array of potential options to satisfy any junk food craving. What do all of these foods have in common? They're all made of refined grains, in addition to other nutritionally deficient ingredients. Refined grains do not offer the same nutritional benefits as whole grains. The process by which refined grains are produced removes fiber, iron, vitamins and other nutrients,

according to the American Heart Association

. Examples of refined grains include white flour, corn flour and white rice. Not only have Americans turned to unhealthier grains for a greater share of their calories; modern wheat is also less nutritious than heritage grain varieties.

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As Americans increasingly eat out at restaurants more and consume more processed foods, salt intake has steadily increased across all age groups. The average American between ages 20 and 74 consumed close to 1,500 mg more sodium per day in 2006 than in 1971,

according to the Institute of Medicine of the National Academies

. The Centers for Disease Control and Prevention (CDC) recommends everyone ages 2 and up consume less than 2,300 mg per day, which is about a teaspoon a day. Some people with certain health risks, such as diabetes or high blood pressure, should limit that further to 1,500 mg per day. Eating too much salt increases water intake in the body, which leads to high blood pressure. Kidneys work overtime to deal with the excess sodium, and the increased blood volume puts a strain on the heart and blood vessels. At worst, a lifetime of a sodium surplus could lead to heart failure or stroke,

according to the Harvard School of Public Health


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In 1929, presidential candidate Herbert Hoover ran under the slogan "a chicken in every pot and a car in every garage." These items might seem common enough today, but Hoover was basically promising what were then considered luxuries to every American household. At the time of Hoover's campaign, "the few chickens raised for meat were sold directly to high-end restaurants, first-class dining cars, and luxury caterers,"

according to the Smithsonian Museum of American History

. Chickens were instead kept for their eggs, which are a valuable source of protein and other nutrients. Egg consumption peaked mid-century, and has been in decline ever since. The overblown connection between cholesterol in eggs and heart disease certainly contributed to Americans turning their back on eggs. But a decline in prices of another protein source, specifically chicken, also contributed to eggs falling out of favor. In the last half of the 20th century, poultry consumption went up more than three-fold, according to USDA data. Red-meat consumption saw a steady decline over the same period, with Americans eating roughly 10 percent fewer pounds per capita every year.

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