Here’s some bad news for health conscious people. If their parents and grandparents gorged on unhealthy food, they may face an exaggerated risk of weight gain. That’s the finding of a new mouse study. It’s not yet been confirmed that the same is true in people. But it was a concern over human risks that prompted the new study.
Too little exercise and eating too many calories are root causes of obesity. However, in the past few years, scientists have begun to explore the role of our DNA. Some genes may play a role in making people fat. For instance, studies have shown that some genes can make a person’s body burn calories less efficiently. People with these “fat” genes could find it hard to lose weight.
The latest study, conducted in Australia, adds to those depressing data. It shows that the tendency of some people to become overweight may trace to what their parents or even grandparents ate long before they were born.
That new experiment was conducted in two parts. First, the researchers bred a group of obese male mice with lean females. They also bred a control group with each other. Here, both males and females had a healthy weight.
When male mice that had an obese father were given junk food to eat, they developed a lot of problems. They had higher-than-normal levels of blood sugar, or glucose. They also had an excess of the hormone insulin in their blood. Perhaps worst of all, their livers accumulated too much fat. All of these conditions are generally found in people who are obese, have metabolic syndrome or have diabetes.
Female mice born to obese fathers were not affected. The male mice that had a lean father also showed no problems.
The DNA in the two sets of offspring were the same. This meant that the genes of those obese fathers were not the problem, says Jennifer Cropley. She works at the Victor Chang Cardiac Research Institute in Darlinghurst, Australia. The animals’ genes had not been directly to blame, her team found. Their symptoms of metabolic syndrome instead traced to how or when certain genes were allowed to operate.
Cropley studies epigenetics. It’s the branch of science that looks at how things in the environment, including diet, can affect little “tags” on genes. These tags work like switches to turn genes on and off. And it was those external switches that were somehow altered, Cropley’s group discovered.
What’s more, it wasn’t just the sons of the obese dads that showed this metabolic problem. The grandsons, too, developed the same problems after they ate junk food for a while. And this held even for mice whose fathers had eaten well and maintained a healthy weight.
These findings will be published soon in the journal Molecular Metabolism.
Why was this just a male thing?
When the scientists realized it wasn’t genes themselves that were making the next generation of mice fat, they wondered what was going on. What might be happening during mating that made sons and the grandsons of obese male mice so vulnerable?
They decided to look at the sperm of the male mice. RNA is a type of genetic material. It acts like a watchdog, deciding whether or not its gene gets turned on. The RNA in sperm was different in the sons with obese fathers than in sons with lean dads. “It was always thought that sperm just have DNA,” says Cropley. “But in fact, they have RNA molecules,” she says.
This study will change people’s attitudes toward pregnant women, Cropley predicts. “If you’re pregnant, you’re told you should eat well and not drink or smoke,” says Cropley. “Our results prove that contributions of dads might be just as important.”
Laura Dearden is a researcher at the University of Cambridge in England. There, she studies how early-life factors can affect someone’s appetite. Dearden says the study sends out a warning message: “If you are aware of a history of obesity in your family tree, even if your parents aren't obese, you should be careful what you eat.”
Michelle Holland is a researcher at Blizard Institute in London, England. Like Cropley, she studies epigenetics. Holland says scientists always thought this kind of “non-genetic inheritance” did not occur in mammals. But studies such as this have begun to prove that the previous “assumption was wrong.”
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blood sugar The body circulates glucose, a type of simple sugar, in blood to tissues of the body where it is used as a fuel. The body extracts this simple sugar from breakdown of sugars and starches. However, some diseases, most notably diabetes, can allow an unhealthy concentration of this sugar to build up in blood.
calorie The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food.
cardiac arrhythmia An irregular heartbeat. There are several types of arrhythmias; the heart can beat too fast, too slow or in a pattern that’s not normal. Some arrhythmias are mild and have little if any effect; others can be life-threatening.
control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.
diabetes A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.
DNA (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
environment The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.
epigenetic changes Molecular switches that can turn a gene on or off. Methyl groups — chemical clusters each made of one carbon and three hydrogen atoms — latch onto DNA near a gene. It’s these methyl groups that can alter the programmed activity of a gene, turning it on or off. Individuals can acquire an epigenetic change at any time during their lives
fat A natural oily or greasy substance occurring in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat is also a vital nutrient, though it can be harmful to one’s health if consumed in excess amounts.
fatty liver disease A condition that results when too much fat builds up inside the liver. People who are obese or drink too much alcohol risk developing this condition. Left untreated and allowed to worsen, it can eventually lead to life-threatening liver failure.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for producing a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
genetic Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.
generation A group of individuals born about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet -are referred to as belonging to a particular generation of humans. The term is sometimes extended to inanimate objects, such as electronics or automobiles.
glucose A simple sugar that is an important energy source in living organisms. It is half of the molecule that makes up table sugar (also known as sucrose).
hormone (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
insulin A hormone produced in the pancreas (an organ that is part of the digestive system) that helps the body use glucose as fuel.
liver An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, breakdown harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.
mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding the young, and (typically) the bearing of live young.
metabolic syndrome A health condition made up of any three of the following six problems: obesity, high blood pressure, insulin resistance, high levels of bad fats alongside low good cholesterol, extra blood components that cause inflammation and extra blood components that lead to clots. People with metabolic syndrome have an increased risk of developing diabetes or heart disease.
metabolism The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
obesity Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.
RNA (short for ribonucleic acid) A single-stranded molecule inside most of cells that performs a number of functions, including producing protein. RNA molecules can also play a role in the expression of some genes.
sperm The reproductive cell produced by a male animal (or, in plants, produced by male organs). When one joins with an egg, the sperm cell initiates fertilization. This is the first step in creating a new organism.
symptom A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.
JOURNAL: J. Cropley et al. Male-lineage transmission of an acquired metabolic phenotype induced by grand-paternal obesity. Molecular Metabolism. Accepted June 16, 2016. doi: 10.1016/j.molmet.2016.06.008.