What should we eat? Answers abound in the international media, all of which rely on their interpretation of recent medical literature to come up with recommendations for the healthiest diet. But what if you could answer this question at a molecular level - what if you could find out how our genes respond to the foods we eat, and what this does to the cellular processes that make us healthy - or not? That's precisely what biologists at the Norwegian University of Science and Technology have done.
If you could ask your genes to say what kinds of foods are best for your health, they would have a simple answer: one-third protein, one-third fat and one-third carbohydrates. That's what recent genetic research from the Norwegian University of Science and Technology (NTNU) shows is the best recipe to limit your risk of most lifestyle-related diseases.
Food affects gene expression
NTNU researchers Ingerid Arbo and Hans-Richard Brattbakk have fed slightly overweight people different diets, and studied the effect of this on gene expression. Gene expression refers to the process where information from a gene's DNA sequence is translated into a substance, like a protein, that is used in a cell's structure or function.
"We have found that a diet with 65% carbohydrates, which often is what the average Norwegian eats in some meals, causes a number of classes of genes to work overtime," says Berit Johansen, a professor of biology at NTNU. She supervises the project's doctoral students and has conducted research on gene expression since the 1990s.
"This affects not only the genes that cause inflammation in the body, which was what we originally wanted to study, but also genes associated with development of cardiovascular disease, some cancers, dementia, and type 2 diabetes -- all the major lifestyle-related diseases," she says.
Common dietary advice and chronic disease
These findings undercut most of the underpinnings for the diets you've heard will save you. Dietary advice abounds, and there is a great deal of variation as to how scientifically justified it is. But it is only now that researchers are figuring out the relationship between diet, digestion and the effect on one's health and immune system - so they can now say not only what kinds of foods are healthiest, but why.
"Both low-carb and high-carb diets are wrong," says Johansen. "But a low-carb diet is closer to the right diet. A healthy diet shouldn't be made up of more than one-third carbohydrates (up to 40 per cent of calories) in each meal, otherwise we stimulate our genes to initiate the activity that creates inflammation in the body."
This is not the kind of inflammation that you would experience as pain or an illness, but instead it is as if you are battling a chronic light flu-like condition. Your skin is slightly redder, your body stores more water, you feel warmer, and you're not on top mentally. Scientists call this metabolic inflammation.
A powdered diet
Johansen and her colleagues conducted two studies. The first was to determine what type of research methods they would use to answer the questions they had. In the pilot study (28 days) five obese men ate real food, while in the second study, 32 slightly overweight men and women (mainly students) ate specially made powdered food.
Participants in the latter study were randomly assigned to go six days on a diet with 65 percent of calories from carbohydrates, with the rest of the calories from protein (15 percent) and fat (20 percent), then a week with no diet. Then came the six days on a diet with half the carbs and twice as much protein and fat as in the first diet. There were blood tests before and after each dieting period.
The amount of food each person ate was calculated so that their weight would remain stable and so that equal portions were consumed evenly over six meals throughout the day.
The researchers had help developing diets from Fedon Lindberg, a medical doctor who specializes in internal medicine and who promotes low-glycaemic diets, Inge Lindseth, an Oslo dietician who specializes in diabetes, and Ann-Kristin de Soysa, a dietician who works with obese patients at St. Olavs Hospital in Trondheim.
"We wanted to know exactly what the subjects were getting in terms of both macro- and micronutrients," says Johansen, -"A tomato doesn't contain a consistent amount of nutrients, or antioxidants, for example. So make sure we had a handle on the health effects, we had to have accurate accounting of nutrients. That's why we chose the powdered diets for the main study."
Solving the control problem
Diet studies that compare different diets with different amounts of fat are often criticized with the argument that it is difference in the amount of omega-3 fatty acids that causes the health effects, not the rest of the food intake.
The researchers addressed this problem by having the same amount of omega-3 and omega-6 in both diets, although the amount of fat in general was different in the diets that were tested. The researchers also avoided another common problem: the natural variation in gene expression between humans.
"Each of our study subjects was able to be his or her own control person, " Johansen says "Every subject was allowed to go on both diets, with a one-week break in between the diets, and half began with one diet, while the rest started with the other diet."
Blood tests were conducted before and after each diet period. All of the measurements of changes in gene expression were done so that each individual's difference in gene expression was compared with that person alone. The results were then compiled.
Johnson says the studies resulted in two important findings. One is the positive effect of many meals throughout the day, and the details about the quality and composition of components in an optimal diet, including omega-3 and omega-6 fatty acids. The second is that a carbohydrate-rich diet, regardless of whether or not a person overeats, has consequences for genes that affect the lifestyle diseases, she says.
A way to measure genetic temperature
Throughout the study, researchers surveyed the extent to which various genes were working normally or overtime. An aggregate measure of the results of all of this genetic activity is called gene expression. It can almost be considered a measurement of the genetic temperature of the body's state of health.
"We are talking about collecting a huge amount of information," says Johansen.
"And it's not like there is a gene for inflammation, for example. So what we look for is whether there are any groups of genes that work overtime. In this study we saw that an entire group of genes that are involved in the development of inflammatory reactions in the body work overtime as a group."
It was not only inflammatory genes that were putting in overtime, as it would turn out. Some clusters of genes that stood out as overactive are linked to the most common lifestyle diseases.
"Genes that are involved in type 2 diabetes, cardiovascular disease, Alzheimer's disease and some forms of cancer respond to diet, and are up-regulated, or activated, by a carbohydrate-rich diet," says Johansen.
Johansen is not a cancer researcher, and is not claiming that it is possible to eliminate your risk of a cancer diagnosis by eating. But she thinks it is worth noting that the genes that we associate with disease risk can be influenced by diet.
"We're not saying that you can prevent or delay the onset of Alzheimer's if you eat right, but it seems sensible to reduce the carbohydrates in our diets," she suggests.
"We need more research on this," Johansen adds. "It seems clear that the composition and quantity of our diets can be key in influencing the symptoms of chronic disease. It is important to distinguish between diet quality and quantity, both clearly have very specific effects."
The body's arms race
Johansen argues that diet is the key to controlling our personal genetic susceptibility to disease. In choosing what we eat, we choose whether we will provide our genes the weapons that cause disease. The immune system operates as if it is the body's surveillance authority and police. When we consume too many carbohydrates and the body is triggered to react, the immune system mobilizes its strength, as if the body were being invaded by bacteria or viruses.