Home Tags Posts tagged with "body mass index"
body mass index
Mathematician Nick Trefethen claims that those who are short of stature may be fatter than they thought.
Oxford academic Nick Trefethen believes the body mass index (BMI) formula traditionally used to work out if someone is overweight is flawed – and he has come up with his own.
And he found short people are actually more overweight than they think they are, while tall people are not as overweight as they are being told.
Prof. Nick Trefethen says the existing formula falls down because it underestimates how much natural bulk taller people have.
As a result, it overestimates how well-padded short people should be. By his theory, singer Lily Allen, who is just 5ft 2in, is not as slim as she might be led to believe.
While his calculations tip the scale in favor of model Sophie Dahl, who stands 5ft 11in. The BMI formula is used by doctors up and down the country to work out if someone is overweight or obese and so at risk of problems from high blood pressure to heart disease.
A BMI of between 18.5 and 24.9 is normal. Less than 18.5 would see a person classed as underweight, while 25 to 29.9 is considered overweight.
Oxford academic Nick Trefethen believes the BMI formula traditionally used to work out if someone is overweight is flawed
A mark of 30 or above means a person is obese. It is calculated by dividing weight in kilograms by height in metres squared and tells someone if they are of a healthy weight, underweight, overweight or obese.
But under Prof. Nick Trefethen’s new version, the weight in kilograms is multiplied by 1.3. The answer is then divided by a person’s height to the power of 2.5, rather than height squared.
The professor insists his formula is far from simply an academic exercise – as the results could affect millions of people.
Roughly speaking, each person 6ft tall would lose a point from their BMI reading. Those who are 5ft, however, would see the new formula add a point – enough to send them from being merely overweight to obese.
Experts already question the use of BMI as an indicator of health as it fails to distinguish between muscle and fat and can lead to athletes at peak fitness being deemed obese.
Prof. Nick Trefethen said it would be wrong for him to push for his formula to be adopted, but he says the NHS should justify its use of the current calculation.
He said: “The NHS relies on the BMI pervasively in all of its public discussions of obesity. We deserve an explanation of what justification they have for using this formula.”
New research has shown that when placed under stressful situations, men rate larger women as more attractive.
British researchers found that men exposed to tasks that were designed to put them under pressure preferred a wider range of female body sizes.
They conclude that stress can act to alter judgments of potential partners.
The work by a team from London and Newcastle is published in the open access journal Plos One.
“There’s a lot of literature suggesting that our BMI (body mass index) preferences are hard-wired, but that’s probably not true,” said co-author Dr. Martin Tovee, from Newcastle University.
New research has shown that when placed under stressful situations, men rate larger women as more attractive
Dr. Martin Tovee and his colleague, Dr. Viren Swami, have previously researched what factors could alter BMI preferences, including publishing a paper in the British Journal of Psychology on the effect of hunger, and the influence of the media.
But through this new work they aimed to investigate whether known cross-cultural differences in body size preferences linked to stress were also mirrored in short-term stressful situations.
“If you look at environments where food is scarce, people’s preferences for body size in a potential partner are shifted. [The preference] appears to be much heavier compared to environments where there’s plenty of food and a much more relaxed atmosphere,” he explained.
“If you’re living a far more stressful, subsistence lifestyle, you’re going to have higher stress levels.”
To simulate heightened stress, a test group of men were placed in interview and public speaking scenarios and their BMI preferences compared against a control group of non-stressed men.
The results indicated that the change in “environmental conditions” led to a shift of weight preference towards heavier women with the men considering a wider range of body sizes attractive.
“These changes are comparatively minor in comparison to those you get between different [cross-cultural] environments. But they suggest certain factors which might combine with others and cause this shift,” Dr. Martin Tovee said.
The research supports other work that has shown perceptions of physical attractiveness alter with levels of economic and physiological stress linked to lifestyle.
“If you follow people moving from low-resource areas to higher resource-areas, you find their preferences shift over the course of about 18 months. In evolutionary psychology terms, you try to fit your preferences to what works best in a particular environment,” said Dr. Martin Tovee.
Moreover, the researchers were keen to emphasize how fluctuating environmental conditions could alter the popular perception of an “ideal” body size.
“There’s a continual pushing down of the ideal, but this preference is flexible. Changing the media, changing your lifestyle, all these things can change what you think is the ideal body size,” he said.
The periods of eating very little or nothing may be the key to controlling chemicals produced by the body linked to the development of disease and the ageing process.
This backs up recent studies on animals fed very low-calorie diets which found the thinnest (without being medically underweight or malnourished) are the healthiest and live the longest.
The key, say researchers at the University of Southern California’s Longevity Institute, is the hormone Insulin-Like Growth Factor 1 (IGF-1).
IGF-1 and other growth factors keep our cells constantly active. It’s like driving with your foot on the accelerator pedal, which is fine when your body is shiny and new, but keep doing this all the time and it will break down.
According to Professor Valter Longo, director of the Longevity Institute, one way to take the foot off the accelerator, and reduce IGF-1 levels dramatically – as well as cholesterol, and blood pressure – is by fasting.
“You need adequate levels of IGF-1 and other growth factors when you are growing, but high levels later in life appear to lead to accelerated ageing,” he says.
“The evidence comes from animals such as the Laron mice we have bred which have been genetically engineered so they don’t respond to IGF-1. They are small but extraordinarily long-lived.”
The periods of eating very little or nothing may be the key to controlling chemicals produced by the body linked to the development of disease and the ageing process
The average mouse has a life span of two years – but the Laron typically live 40% longer. The oldest has lived to the human equivalent of 160. They are immune to heart disease and cancer and when they die, as Prof. Valter Longo puts it: “They simply drop dead.”
Trying various fasts, for three days straight, and for two days a week, for six weeks, you can see dramatic results. Not only weight loss, but your cholesterol levels and blood pressure improve. These findings chime with recent reports that reaching a “healthy” Body Mass Index (BMI) may not be enough – we need to be as slim as possible to reduce our risk of illness.
The reason experts haven’t emphasized this is that they don’t want to trigger eating disorders or demotivate the overweight trying to get into the healthy weight range. There is only so long, however, we can shy away from this because the evidence keeps mounting.
Matthew Piper, of the Institute of Healthy Ageing, University College London, says: “Studies on monkeys show if we restrict the diet there is a delay in the onset of cancer, coronary heart disease and diabetes in later life as well as staving off dementia.”
Reducing our food intake over months or years could boost lifespan by 15 to 30%, experts believe.
Although the Scarsdale Medical Diet was a hit for the Seventies audience relatively new to slimming, it is brutal physically and mentally. But Dr. Rachel Thompson, of the World Cancer Research Fund, says: “Whatever your BMI, if it goes up so does your cancer risk. It’s better to be at the lower end of the healthy BMI range if possible.”
For every two points you jump up the scale, your risk of postmenopausal breast cancer goes up 3%.
The Scarsdale Diet is a high-protein, low-carbohydrate mix with a fixation on grapefruit.
Unlike other high-protein diets that allow you to stuff yourself with fatty bacon and cheese, this diet imposes strict limits.
Breakfast is always half a grapefruit and a piece of toast with no butter or jam. Lunch on day one is cold cuts of meat with all fat removed and a tomato.
Supper is fish with salad and a piece of bread followed by more grapefruit. You must also drink lots of water and, thankfully, black tea and coffee are allowed.
The first days are a blur of dry toast, fruit and sliced tomatoes and meat.
US researchers have found that the obesity problem may be much worse than previously thought.
Experts said using the Body Mass Index (BMI) to determine obesity was underestimating the issue.
The US study, published in the journal PLoS One, said up to 39% of people who were not currently classified as obese actually were.
The authors said “we may be much further behind than we thought” in tackling obesity.
BMI is a simple calculation which combines a person’s height and weight to give a score which can be used to diagnose obesity. Somebody with a BMI of 30 or more is classed as obese.
According to the US Centers for Disease Control, at least one in three Americans are obese.
Other ways of diagnosing obesity include looking at how much of the body is made up of fat. A fat percentage of 25% or more for men or 30% or more for women is the threshold for obesity.
According to the US Centers for Disease Control, at least one in three Americans are obese
One of the researchers Dr. Eric Braverman said: “The Body Mass Index is an insensitive measure of obesity, prone to under-diagnosis, while direct fat measurements are superior because they show distribution of body fat.”
The team at the New York University School of Medicine and the Weill Cornell Medical College, New York, looked at records from 1,393 people who had both their BMI and body fat scores measured.
Their data showed that most of the time the two measures came to the same conclusion. However, they said 539 people in the study – or 39% – were not labeled obese according to BMI, but their fat percentage suggested they were.
They said the disparity was greatest in women and became worse when looking at older groups of women.
“Greater loss of muscle mass in women with age exacerbates the misclassification of BMI,” they said.
They propose changing the thresholds for obesity: “A more appropriate cut-point for obesity with BMI is 24 for females and 28 for males.”
A BMI of 24 is currently classed as a “normal” weight.
“By our cut-offs, 64.1% or about 99.8 million American women are obese,” they said.
It is not the first time BMI has been questioned. A study by the University of Leicester said BMIs needed to be adjusted according to ethnicity.
Israel passed a law banning models from advertisements or fashion shows if they measure less than 18.5 on the body mass index (BMI).
The new law is part of an effort to promote health for women of all sizes, and to stop glorifying the ultra-thin.
“Beautiful is not underweight,” says Rachel Adato, one of the creators of the bill.
In recent years, much attention has been paid to how women are portrayed in the media, whether it’s an overly airbrushed magazine model with an impossibly slim waist, or a TV starlet with protruding collar bones.
In an era when pro-anorexia communities congregate on social media sites like Pinterest, it’s no wonder that lawmakers are concerned with women’s body image.
For sure, reducing the number of images that portray women as very thin is beneficial, says Claire Mysko, director of Proud2BeMe, a website created with the National Eating Disorders Association (NEDA) to promote healthy body image.
“There is a danger in being constantly exposed to one image of beauty,” Claire Mysko says.
“There is a serious lack of body diversity in the media. People are not seeing themselves and their bodies reflected.”
Israel’s law may be the catalyst needed to help make change. But others say it could make things worse.
Many magazine editors, modelling agents and casting directors say they want to use more diverse models, but can’t because of industry expectations – with each blaming the other group for setting the tone.
Israel passed a law banning models from advertisements or fashion shows if they measure less than 18.5 on the body mass index
“They all feel trapped into producing what nobody individually espouses,” says Amanda Mears, author of Pricing Beauty: The Making of a Fashion Model.
“Everyone felt individually powerless.”
Regulating the types of models that can be used may be a good way to “shock” the system into making changes, she says.
However, Amanda Mears, along with many other experts on eating disorders and body image, worry that the law is flawed.
“Bodies come in different shapes and sizes, and the very idea that there is a concrete qualifying number, and if someone can match it they’re considered healthy, is wrong,” Amanda Mears says.
BMI, a ratio of height to weight, is best used as a way to measure the average size of groups of people, but is not a good indicator of personal health, says Margo Maine, a clinical psychologist who has specialized in eating disorders.
“It’s arbitrary,” Margo Maine says.
“In the past I would have welcomed [the law] but I am a little leery of the judgment about the correct body type.”
Limiting the types of bodies that are permitted to model or considered attractive can backfire, says Matthew Johnson, director of education at the Media Awareness Network, a media education programme in Canada.
“What would be more effective would be encouraging a wider variety of body shapes on TV and in media in general.”
Otherwise, the message is not to celebrate bodies of all shapes and sizes, but to reject extreme thinness.
“We have reduced women to their size,” says Dr. Margo Maine, author of The Body Myth.
“By targeting women who are thin, whether they have an eating disorder or are naturally thin, we are focusing on the individual instead of challenging the culture that buys into it.”
Thin women may have an easier go of it than fat women, but they’re still subject to attacks about their size. Catherine, the Duchess of Cambridge, is subjected to constant speculation about her health and comments about her weight.
Angelina Jolie’s Oscar appearance last month set Twitter alight with criticisms of her thin frame. “Angelina Jolie looks like her arms are ready to snap in half at any moment. Gross,” wrote one user.
Speaking out against very thin star celebrities can feel like a satisfying blow against unrealistic body standards, says Raegan Chastain.
As an advocate for fat acceptance she has often heard people criticize women for being too thin.
Still, she warns those trying to come to terms with their own size to leave other people out of it.
“If you want to push against standards, you don’t do that by bashing people,” Raegan Chastain says.
“You can’t look at someone and tell how healthy they are. Weight and health are two separate things.”
With that in mind, NEDA has advocated that models be screened for eating disorders, but not that they be prohibited from working based on a size and weight limit.
They’ve also launched Proud2BeMe, an extension of a Dutch website designed as a safe space to discuss body issues and health concerns.
“There are people who are naturally thin and people who are naturally heavier, and we need to accept a diversity,” Claire Mysko says.
“That’s the goal: not to define one body type as attractive and another type as unattractive.”
• Spain: Madrid fashion week restricted models who have a BMI of less than 18 (2006)
• Italy: Government instituted a self-policing code of conduct for the fashion industry, including requiring medical proof that models do not have eating disorders (2006)
• UK: the Advertising Standards Authority issued guidelines about the use of digitally manipulating photos, saying they will stop ads that are misleading, including those that portray extreme thinness (2011)