(Disponível em português)
Is there an ideal diet? This is a crucial question in terms of human health, but it has proven difficult to answer. Nowadays, diets are still based on empirical know-how, shaped by generations of experience in the field. However, a new study now suggests that genomics could revolutionize the way that protein composition of a diet is determined.
An international team of scientists, which includes two neuroscientists from the Champalimaud Centre for the Unknown (CCU), in Lisbon, Portugal, has made a surprising discovery: inside the genome of each animal species lies the information required to determine the healthiest dietary protein composition for that species. This result, which has been published in the March 7th edition of the journal Cell Metabolism, may have important implications not only for humans but also for animals husbandry.
Proteins are the building blocks of living tissues. Without these biological molecules, there is no life. Animal cells are protein-making machines, but for that they need to get the basic ingredients – the amino acids that compose these molecules – from food: herbivores from the plants they eat, carnivores from animal protein. As cartoon character Mafalda once asked her father (in one of those famous comic strips by Argentinian cartoonist Quino): “Does that mean cows are the middleman between grass and us?”
The diets which are currently considered to be the healthiest for farm-raised animals, for laboratory animals such as fruit flies and mice, and also for humans, have been shaped by centuries of empirical observation, but they are by no means perfect. We now know, for instance, that eating too much protein, while enhancing an animal’s reproductive capacity, reduces its lifespan.
Could there be a way to design a diet that would guarantee a balance between these two aspects of an animal’s health? More to the point, the authors of the new study wanted to know whether there could be an objective way of optimizing the protein content of a diet in order to increase an animal’s fertility without curtailing its life – and without making it feel hungry.
This is not an easy problem to solve. Proteins are made of sequences of amino acids, and there are 20 different amino acids to pick from. “Optimizing amino acid intake is a 20-dimensional problem”, the authors write in their paper.
Simple arithmetics
When we use a recipe to cook a dish, we have to blend in the right proportions of each ingredient – 200 grams of this, 50 grams of that, points out CCU’s Samantha Herbert, coauthor of the study.
But in the case of a recipe based on 20 amino acids, what should those proportions be? The team hypothesized that each species will have its own amino acid needs, and that these needs are encoded in the genome. And so they decided to test a diet in which the ratio of each amino acid was obtained from the number of times that the genetic code of that amino acid was repeated along the thousands of protein-coding genes in that species.
That set of protein-coding genes is what specialists call the “exome” – in contrast to the rest of the genetic material, that doesn’t code for proteins. And thanks to extant genetic sequencing technologies, deriving information about a species’ exome has become a very simple and quick process from the technical point of view.
The authors, led by Matthew Piper and Linda Partridge, of University College London (and including scientists from Germany, China, and Australia), then derived the respective amino acid ratios from the fruit fly and mouse genomes.
“This is a very simple mathematical operation”, says Samantha Herbert. She and Carlos Ribeiro, principal investigator at the CCU’s Behavior and Metabolism Lab, were in charge of the part of the study that asked what the effects of this “exome-matched” diet would be on the health and feeding behavior of fruit flies.
Their following step consisted of comparing this diet with different standard diets which are used to feed these animals in labs all over the world.
The scientists were very surprised by the results, given the simplicity of the approach. “We found that the genetic sequence, stripped of all its information except the amino acid ratios, was sufficient to design a diet better [in terms of the fertility/longevity balance] than any others we tested”, explains Samantha Herbert.
According to Samantha Herbert, this information may be sufficient to optimize the dietary protein content because, for each species, and even at the individual level, the proportions of the amino acids in the exome represent a common denominator of the protein needs for all the tissues and organs in the body.
The team observed, in the two species they tested, that the exome-matched diet increased reproductive health without reducing lifespan. Also, the diet promoted the animals’ growth and increased their feeling of satiety, which is an indicator of a diet’s efficiency.
new diet alters fly behavior
But do the animals really like this food? In the case of the fruit flies, says Samantha Herbert, “we kept them on the various diets for several days, and then we fed them yeast, which is normal fly food. And we found that the flies that had been previously fed the exome-matched diet ate less yeast than the others.”
In other words, the CCU scientists showed that the insects’ behavior itself changed under the effect of the new diet. “The ‘exome-matched’ fly food made the flies feel more full. In part this is because they were eating more of it, which may in turn be due to the the fact that they could tell it was better for them”, adds Samantha Herbert.
Could these results be valid for other species, including humans? “In theory, this strategy could work with any animal”, replies Samantha Herbert. For instance, to design the most efficient diet for farm-raised animals – which would also be the most economically adapted for the farmers who raise them.
And what about humans, for example in the fight against obesity? “The challenge with human beings”, says Samantha Herbert, “is that it’s difficult to do the experiments. The food we’re talking about here is sort of a jelly, something that people would certainly not be willing to eat” to test its effects. But who knows? After all, protein “porridges” are already commercially available for weight control. And a great number of people rely on this kind of artificial food for their daily diet.
In any case, the results of the study suggest that there is “a powerful method, with strong effects, that could revolutionize diets”, says Samantha Herbert. “I like being optimistic, so I think that maybe we are closer than we imagine to developing an ideal diet, which could guarantee people’s good health throughout their life.”
Ana Gerschenfeld works as a Science Writer at the Science Communication Office at the Champalimaud Neuroscience Programme
Edited by: Catarina Ramos(Science Communication office). Photo credit: lyzadanger (Creative Commons Attribution-ShareAlike 2.0)
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