Research We’re Reading
NRI scientists are reading latest findings in the field of nutrigenomics to share new information with you.
From the desk of: Sergey A. Krupenko, Ph.D.
Life expectancy keeps growing in developed countries, approaching 90 years on average in some. There is a forecast that more than 50 percent of girls born in the U.S. after 2010 will live to become 100 years or even older, and that the first person to live up to 150 years has already been born. Perhaps most people are curious about which factors define that people live longer. Obviously, genetic background plays a significant role in a person’s natural longevity. What about diet? Can nutrients help to prolong our life? One of the principal dietary factors influencing our overall health status is calorie consumption. Intuitively, limiting calories to some extent would be expected to improve health conditions and, as such, seems promising for longer life. Indeed, there is a common belief in modern society that skinny people are healthier than obese people. But, does it mean they will live longer? Numerous research papers beginning in the late 1990s and early 2000s indicate that calorie restriction extends lifespan in a wide spectrum of organisms. However, a paper published last year indicates that the issue regarding the influence of calorie restriction on lifespan might not be so simple.
In this study, an international research team led by scientists from the University of Sydney used 25 diets differing in protein, carbohydrate, fat content and energy density to feed mice. The team aimed to correlate macronutrient intakes to longevity, in particular testing the extent to which lifespan in ad libitum-fed (unlimited food) mice is determined by calorie intake per se or by the balance of protein to carbohydrate. With no surprise, this study showed a very complex interplay between dietary protein, carbohydrates, total energy intake and lifespan. Using a very sophisticated mathematical approach, researchers were able to untangle these complex data. They found that lifespan was greatest for animals whose foods were low in protein and high in carbohydrate, and it was not influenced by total calorie intake. This study also identified the molecular target, which is likely responsible for translating the dietary ratio of proteins and carbohydrates to lifespan. A protein kinase mTOR (stands for mammalian target of rapamycin), which regulates several key cellular processes, was activated as dietary ratio between proteins and carbohydrates was shifted towards the former. Since the activation of mTOR is pro-aging, this would explain the life-extending effects of a low-protein, high-carbohydrate diet.
IMPLICATIONS OF THIS STUDY FINDINGS
While it still needs to be confirmed that findings of this study are applicable to humans, they are in line with epidemiological studies showing that low-protein, high-carbohydrate diets are associated with improved health in humans. Accordingly, high-protein diets, widely promoted for weight loss and health, should be taken with precautions. Overall though, rather than specific macronutrients themselves, it is their interactive effects (i.e., balanced diet) that are more important for health and aging.
Excitingly, because mTOR can be targeted by drugs, this also opens a window of opportunity to pharmacological life extension in the future. However, while such an opportunity might be on the horizon, it is still a good idea to limit calorie consumption and engage in regular physical exercises.
From the desk of: Carol L. Cheatham, Ph.D.
As a developmental cognitive neuroscientist, I’m always interested in learning about studies that will inform my work. Recently, I attended the International Conference on Infant Studies where I heard a scientist speak about his research with non-human primates (i.e., monkeys). The studies that he described weren’t just informative—his results stopped me in my tracks! Since I returned home, I have been reading all his papers and I’m excited to share his findings.
In Japan, a scientist by the name of Tetsuro Matsuzawa has been working for 30 years with Ai, a chimpanzee and her offspring. Ai learned at an early age to recognize symbols on a keyboard and to name objects and colors. She and her kids have also been taught numbers and number order. For one number task, these chimpanzees are trained on a touch screen. Numbers from 1 to 9 are presented on a screen in random order and in random places on the screen. The chimps touch the numbers in ascending order to receive a treat.
This is a truly impressive feat in and of itself, however, more amazingly, these chimps can still successfully complete the task when the numbers on the screen disappear behind white boxes the instant they touch the number 1! Let me say that again: the numbers from 1 through 9 come up on the screen in random order and in random places. The chimp’s job is to touch the numbers in order. The instant that the chimp touches the number 1 (see photo A), the other numbers disappear behind white boxes (see photo B), and the chimp must finish the task basically blind. The chimps in this “masked” task are still successful even though they only saw all nine numbers for a split second. To put this in perspective, humans who are tested on this masked task can only touch the first three or four numbers correctly. Mind you, this skill cannot be taught. The brain has to encode the numbers and their positions in a flash and be able to recall the position of numbers. Why don’t humans have such a flash memory? Dr. Matsuzawa hypothesizes that language gets in our way. Basically, our brains get bogged down by attaching words to the numbers—a problem that the chimps do not have!
You can watch the chimps perform both the numbers and masked numbers tasks here. There are also videos of human subjects attempting the same tasks, but with far less success.
Finding out about this research has had me devising ways to test it in humans as well as trying to explain it in chimps. Why would chimps need flash memory? Can the human brain work similarly? How would we test that question when our lives are so tied to language? As I continue my work in cognitive development and decline, I will ponder Dr. Matsuzawa’s work with these chimpanzees and their extraordinary recall ability.
From the desk of: Karen D. Corbin, Ph.D., R.D.
As a registered dietitian, I am often asked: “What do you think about artificial sweeteners?” My answer is always the same: “Since they are artificial and not enough research has been conducted to know for certain if they can be harmful, I suggest using them in moderation, learning to drink beverages that are naturally sugar-free, or using regular sugar instead but in moderation.” New research published in the journal Nature indicates a negative impact of artificial sweeteners on the helpful bacteria that live in our intestines. The findings were intriguing and provide one important piece of the puzzle to help better understand the role of these food additives on health.
Artificial sweeteners have been shown to have beneficial effects on weight and metabolism, while other studies have shown the opposite. Despite this controversy, the Food and Drug Administration has approved six different artificial sweeteners for use in the United States. Most artificial sweeteners pass through the intestinal tract without being digested, making them available for processing by the bacteria that reside normally in the gut. These bacteria are very important for processing nutrients and can affect our metabolism and health.
A group of scientists at the Weizmann Institute of Science in Israel wanted to find out if artificial sweeteners affect the types of bacteria in the gut and, if so, what the impact is on metabolism. In mice, the scientists found that artificial sweeteners lead to insulin resistance and an imbalance of bacteria in the gut (dysbiosis), compared to water alone or water with natural sugars like glucose or sucrose. When gut bacteria from mice fed artificial sweeteners were transferred to mice that had no bacteria in their gut, the same harmful metabolic effects occurred.
WHY IS THIS IMPORTANT?
This strongly suggested that the harmful metabolic effects of artificial sweeteners were due to their effects on the gut bacteria. In non-diabetic humans, the scientists also found that long-term consumers of artificial sweeteners had many traits characteristic of metabolic syndrome and fatty liver. Importantly, when they fed healthy volunteers who did not normally consume artificial sweeteners an acceptable daily amount of artificial sweeteners for six days, their metabolisms worsened and their gut bacteria changed.
The study was well done, but focused most of its efforts on one specific artificial sweetener, so the findings may not apply equally to all of them. The part of the study where people were asked to consume artificial sweeteners was very small, and some of the people did not have the same response as others.
WHAT THIS MEANS FOR YOU
Although this study does not provide conclusive evidence that all artificial sweeteners are harmful for all people, it does suggest one way that these food additives could have negative health consequences. Moderation still stands as a reasonable course of action.
From the desk of: Steve Zeisel, M.D., Ph.D.
Gut microbes have been making a lot of news lately. As the name implies, these bacteria reside in the intestine and fulfill a variety of functions essential to our health, specifically ensuring that we digest foods properly. But that’s only the beginning. A recent study shows that gut microbes can also determine your weight.
Gut microbes were harvested from 4 pairs of women who were twins. One twin was thin and the other twin in each pair was obese. The microbes were transplanted in mice. The mice getting the microbes from the obese twin became fatter while the mice getting microbes from the paired lean twin did not get fatter.
WHY IS THIS IMPORTANT?
Until recently we did not realize that the microbes that we house in our guts have an important role in nutrition and metabolism. This study demonstrates that obese people have different microbes in their guts than do lean people and these microbes can change our body weights. How do they do this? We do not yet know but perhaps these microbes make calories more available from hard to digest foods, or perhaps they make signals that disturb how we respond to hormones like insulin.
WHAT THIS MEANS FOR YOU
Our gut microbes are influenced by what we eat. Vegetarians have different microbes than do meat eaters. Some foods, like yogurt, contain bacteria and may help change our microbes. Antibiotics used to treat infections, also can make big changes in our bacteria. Babies delivered vaginally are populated with very different bacteria than babies delivered by C-section.