No, the body mass in­dex is not use­less, and not all peo­ple with obe­sity are un­healthy.

The Washington Post Sunday - - OUTLOOK - By Kevin D. Hall Twit­ter: @Kev­inH_PhD Kevin D. Hall is a se­nior in­ves­ti­ga­tor at the Na­tional In­sti­tute of Di­a­betes and Di­ges­tive and Kid­ney Dis­eases at the Na­tional In­sti­tutes of Health, where he is chief of the In­te­gra­tive Phys­i­ol­ogy Sec­tion and creato

Obe­sity has been on the rise world­wide for decades, putting peo­ple at risk for de­vel­op­ing di­a­betes, heart dis­ease and sev­eral forms of can­cer. To­day, two thirds of adults and one third of chil­dren in the United States are over­weight. As the num­bers on the scale get big­ger, so does the diet and weight­loss industry, which is now worth tens of bil­lions of dol­lars. What doesn’t seem to be in­creas­ing, though, is peo­ple’s un­der­stand­ing of obe­sity and how to lose weight. Here are a few of the myths cloud­ing the facts.

1Body mass in­dex is use­less.

The body mass in­dex, or BMI, is a sim­ple and widely used method for clas­si­fy­ing whether a per­son is over­weight or obese. It’s cal­cu­lated by di­vid­ing a per­son’s body weight by height squared, which helps ac­count for the fact that taller peo­ple weigh dis­pro­por­tion­ately more than shorter peo­ple if they have the same per­cent­age of body fat.

BMI is of­ten crit­i­cized be­cause it doesn’t dif­fer­en­ti­ate mus­cle from fat. Mus­cu­lar peo­ple can there­fore er­ro­neously be clas­si­fied as over­weight. For ex­am­ple, Dal­las Cow­boys quar­ter­back Tony Romo’s BMI makes him bor­der­line obese.

But de­spite its lim­i­ta­tions and no­to­ri­ous counter-ex­am­ples, BMI is highly re­lated to body fat and cor­rectly cat­e­go­rizes peo­ple as hav­ing ex­cess body fat more than 80 per­cent of the time. Ad­di­tional sim­ple mea­sure­ments such as waist cir­cum­fer­ence may be even more in­for­ma­tive be­cause they pro­vide in­for­ma­tion about where fat is dis­trib­uted in the body.

2All peo­ple with obe­sity are un­healthy.

The idea that peo­ple with obe­sity can’t be healthy has been re­peated widely. CNN told read­ers that there’s “no such thing” as healthy obe­sity. Forbes called it “a myth.” “You can’t be fit and fat,” Time re­ported.

But in re­al­ity, fat’s lo­ca­tion in the body may be more im­por­tant for health than the to­tal amount of fat. Peo­ple who are “pear-shaped” tend to store fat in their but­tocks and flanks and are at less risk of dis­ease than those who are “ap­ple-shaped” and tend to ac­cu­mu­late fat around the belly. Es­pe­cially bad is the “vis­ceral fat” around the or­gans as well as the fat in the liver. So be­ing obese but pear-shaped may be less risky than be­ing over­weight or nor­mal weight but ap­ple-shaped. This real­iza­tion has led to the re­cent con­cept of “metabol­i­cally healthy obe­sity.”

Ge­net­ics pri­mar­ily de­ter­mine where fat is stored in the body. Men, es­pe­cially those with South Asian eth­nic back­grounds, have a greater pro­por­tion of the dan­ger­ous vis­ceral fat than women. Tar­get­ing the loss of body fat from one re­gion to an­other is dif­fi­cult, but over­all weight loss re­sults in pre­dictable par­al­lel re­duc­tions of all of the var­i­ous fat de­posits.

Ad­di­tion­ally, ex­er­cise may help coun­ter­bal­ance obe­sity’s neg­a­tive ef­fect on health. Phys­i­cally fit and ac­tive peo­ple who are obese have a sim­i­lar or de­creased risk of car­dio­vas­cu­lar dis­ease and death as peo­ple who are less fat but also less fit. There­fore, phys­i­cal in­ac­tiv­ity may be as great a risk to health as obe­sity, and peo­ple should be en­cour­aged to be ac­tive even if it doesn’t re­sult in weight loss.

3Hav­ing a healthy body weight is all about per­sonal re­spon­si­bil­ity and willpower.

Peo­ple of nor­mal weight some­times like to take credit for avoid­ing obe­sity, sug­gest­ing that fat­ness arises from some com­bi­na­tion of glut­tony and sloth. As all those med­i­cal ex­perts on In­ter­net com­ment sec­tions rec­om­mend, just eat less and ex­er­cise more!

Alas, if only such ad­vice were ef­fec­tive. Con­sider ex­er­cise. Even when peo­ple par­tic­i­pate in a su­per­vised ex­er­cise pro­gram, weight loss is much less than would be ex­pected from the calo­ries burned dur­ing ex­er­cise. On av­er­age, ex­er­cis­ing women ex­pe­ri­ence no weight loss, and many peo­ple ac­tu­ally gain weight. This may be the re­sult of com­pen­satory de­creases in other phys­i­cal ac­tiv­i­ties — such as col­laps­ing on the couch for a few hours af­ter a 30-minute run. Al­ter­na­tively, hunger may in­crease, and it doesn’t take much food to off­set the calo­ries ex­pended dur­ing ex­er­cise.

Why not just count calo­ries and eat less? Un­for­tu­nately, even with the best diet-track­ing apps, peo­ple tend to greatly un­der­es­ti­mate how much food they con­sume. Fur­ther­more, calo­rie in­take tends to fluc­tu­ate widely, with swings of­ten ex­ceed­ing 1,000 calo­ries from one day to the next. How would some­one know if they made a dent in their calo­rie in­take us­ing such im­per­fect tools? Of course, mak­ing large calo­rie cuts would be eas­ier to de­tect, and this is what most peo­ple do when they “go on a diet” to lose weight. When this hap­pens, bi­ol­ogy re­sists weight loss by in­creas­ing ap­petite and hunger.

4Di­et­ing causes the body to go into “star­va­tion mode,” slow­ing its me­tab­o­lism and halt­ing weight loss af­ter sev­eral months.

The idea that dieting can ac­tu­ally be coun­ter­pro­duc­tive for weight loss is a trope that ap­pears in just about ev­ery fit­ness pub­li­ca­tion, and warn­ings of the weight-loss plateau abound.

But al­though it’s true that me­tab­o­lism does slow down when peo­ple cut calo­ries, that off­sets less than half of the de­crease in diet calo­ries over the first six months. It takes sev­eral years for meta­bolic slow­ing to fully off­set the av­er­age di­eter’s re­duc­tion in calo­ries and re­sult in a weight plateau. The fact that most peo­ple ex­pe­ri­ence a weight plateau much ear­lier, typ­i­cally af­ter six to eight months of dieting, means that some­thing else must be hap­pen­ing to thwart their con­tin­ued weight loss.

In truth, the dreaded weight plateau is much more likely the re­sult of a grad­ual loss of ad­her­ence to the orig­i­nal plan — peo­ple are ac­tu­ally eat­ing many more calo­ries when their weight loss stalls than when they started to diet. Why this hap­pens is not fully un­der­stood, but bi­ol­ogy prob­a­bly plays a ma­jor role. For ex­am­ple, we know that weight loss re­sults in hor­monal changes that in­flu­ence feel­ings of hunger and full­ness, as well as al­ter how the brain re­sponds to food cues in the en­vi­ron­ment. Food may ac­tu­ally be­come more re­ward­ing. Th­ese changes in­flu­ence over­all food in­take and may oc­cur be­low our level of con­scious aware­ness. Peo­ple, there­fore, may hon­estly re­port that they are stick­ing to their orig­i­nal diet when the weight plateau oc­curs, but ob­jec­tive mea­sure­ments demon­strate oth­er­wise.

5All di­ets are doomed to fail.

“Be­ware of diet,” Slate warns, not­ing that your chance of keep­ing the pounds off is no higher than it is of sur­viv­ing metastatic lung can­cer. Even ac­tress Gwyneth Pal­trow’s Goop life­style Web site warns that most weight-loss ef­forts are doomed.

This myth ex­ists be­cause, sta­tis­ti­cally, most peo­ple tend to re­gain at least some por­tion of their lost weight af­ter a few years. This is es­pe­cially true if they con­sider dieting a tem­po­rary strat­egy for los­ing weight. How­ever, when diet changes are part of a per­sis­tent life­style mod­i­fi­ca­tion, many peo­ple lose weight and keep it off over the long haul.

A re­cent study showed that eight years af­ter adults be­gan a diet and ex­er­cise pro­gram, more than half main­tained weight loss of greater than 5 per­cent — an amount be­lieved to be clin­i­cally ben­e­fi­cial. Fur­ther­more, al­most 40 per­cent of peo­ple lost more than 10 per­cent of their ini­tial body weight af­ter one year, and about 65 per­cent of those main­tained more than 5 per­cent weight loss af­ter eight years.

In ad­di­tion to fre­quent weight mon­i­tor­ing, the se­cret to their suc­cess may be phys­i­cal ac­tiv­ity. Al­though ex­er­cise may not be very ef­fec­tive for in­duc­ing weight loss, it’s of­ten a ma­jor con­trib­u­tor to main­tain­ing lost weight. This may be be­cause, com­pared to los­ing weight, only a rel­a­tively mod­est change in calo­ries is re­quired to keep weight off.

For ex­am­ple, the Na­tional In­sti­tutes of Health’s Body Weight Plan­ner cal­cu­lates that a 40-year-old woman who weighs 200 pounds re­quires a lit­tle more than 1,000 calo­ries to be cut from her daily diet to lose 40 pounds in six months. But sub­se­quently main­tain­ing the 40-pound weight loss re­quires a per­ma­nent change of only about 350 calo­ries per day, which can be at­tained with one hour of daily walk­ing.


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