Study found few 'wonder pills' had randomised clinical trials to back up dietary claims
Diet supplements are often advertised as `extreme fat burners' or `craving quashers'. But evidence used to support these claims simply doesn't add up, a leading U.S nutrition expert has warned.
Professor Melinda Manore from Oregon State University analysed the research used to support hundreds of diet pill claims. She found no evidence that any single product was a 'wonder pill' causing significant weight loss and found some even had detrimental health effects.
'What people want is to lose weight and maintain or increase lean tissue mass,' Prof Manore said. 'There is no evidence that any one supplement does this. And some have side effects ranging from the unpleasant, such as bloating and gas, to very serious issues such as strokes and heart problems.'
Prof Manore looked at supplements that fell into four categories: products such as chitosan (found in shellfish) that block absorption of fat or carbohydrates, stimulants such as caffeine that increase metabolism, products like conjugated linoleic acid that claim to change the body composition and appetite suppressants such as soluble fibres.
She found that many products had no randomised clinical trials examining their effectiveness, and most showed less than a two-pound weight loss benefit compared to the placebo groups.
She added that most research studies did not include exercise. 'I don't know how you eliminate exercise from the equation. 'The data is very strong that exercise is crucial to not only losing weight and preserving muscle mass, but keeping the weight off.'
A few products, including green tea and low-fat dairy supplements were found to have a modest weight loss benefit of 3-4 pounds but most of these supplements were tested as part of a reduced calorie diet.
'For most people, unless you alter your diet and get daily exercise, no supplement is going to have a big impact', Professor Manore said.
As a dietician and researcher, the professor said the key to weight loss is to eat whole grains, fruits, vegetables and lean meats, reduce calorie intake of high-fat foods, and to keep moving.
'Adding fibre, calcium, protein and drinking green tea can help,' she said. 'But none of these will have much effect unless you exercise and eat fruits and vegetables.'
The study is online in the International Journal of Sport Nutrition and Exercise Metabolism.
SOURCE
Another demolition of the recent red meat scare
I pointed out the basic holes in it but another writer has really gone to town on the garbage. Just an excerpt:
Food Frequency Questionnaires: A Test of Superhuman Memory and Saint-like Honesty
To kick this analysis off, let’s take a look at how the study was actually conducted. As the researchers explain, all of the diet data came from a series of food frequency questionnaires (FFQs) that the study participants filled out once every four years, starting in the 1980s and ending in 2006. (If you’re feeling brave, you can read the questionnaire yourself (PDF) and try imagining how terribly the average, non-diet-conscious person might botch their responses.) The lifestyle and medical data came from additional questionnaires administered every two years.
The full text of our study offers some additional details
In each FFQ, we asked the participants how often, on average, they consumed each food of a standard portion size. There were 9 possible responses, ranging from “never or less than once per month” to “6 or more times per day.” Questionnaire items about unprocessed red meat consumption included “beef, pork, or lamb as main dish” (pork was queried separately beginning in 1990), “hamburger,” and “beef, pork, or lamb as a sandwich or mixed dish.” … Processed red meat included “bacon” (2 slices, 13 g), “hot dogs” (one, 45 g), and “sausage, salami, bologna, and other processed red meats” (1 piece, 28 g).
Notice that one of the foods listed under “unprocessed red meat”—and likely a major contributor to that category—is hamburger, the stuff fast-food dreams are made of. Although this study tracked whole grain intake, it didn’t track refined grain intake, so we know right away we can’t totally account for the white-flour buns wrapped around those burgers (or many of the other barely-qualifying-as-food components of a McDonald’s meal). And unless these cohorts were chock full of folks who deliberately sought out decent organic meat, it’s also worth noting that the unprocessed ground beef they were eating probably contained that delightful ammonia-treated pink slime that’s had conventional meat consumers in an uproar lately.
Next, we arrive at this little gem:
The reproducibility and validity of these FFQs have been described in detail elsewhere.
Ding ding, Important Thing alert! As anyone who’s spent much time on earth should know, expecting people to be honest about what they eat is like expecting one of those “Lose 10 pounds of belly fat” banners to take you somewhere other than popup-ad purgatory: the idealism is sweet and all, but reality has other plans.
And so it is with food frequency questionnaires. Ever since these questionnaires were first birthed unto the world, scientists have lamented their most glaring flaw: people tend to report what they think they should be eating instead of what actually goes into their mouth. And that’s on top of the fact that most folks can barely remember what they ate yesterday, much less what they’ve eaten over the past month or even the past year.
As a result, researchers compare the results of food frequency questionnaires with more accurate “diet records”—where folks meticulously weigh and record everything they eat for a straight week or two—to see how the data matches up. If we follow that last quote to the links it references, we end up at one of the validation reports for the food frequency questionnaire used with the Health Professionals Follow-up Study. Here’s where it gets interesting:
Foods underestimated by the FFQs compared with the diet records (ie, the gold standard) included processed meats, eggs, butter, high-fat dairy products, mayonnaise and creamy salad dressings, refined grains, and sweets and desserts, whereas most of the vegetable and fruit groups, nuts, high-energy and low-energy drinks, and condiments were overestimated by the FFQs.
This shouldn’t come as a shocker if we consider human psychology. Unless we literally live in a cave, most of us are constantly inundated with messages about how high-fat dairy, meat, sweets, desserts, and anything delicious and creamy is going to either make us fat or give us a heart attack—while it’s more like hallowed be thy name for fruits and veggies. Is it any wonder that folks tend to under-report their intake of “bad” foods and over-report their intake of the good ones? Who wants to admit—in the terrifying permanency of a food questionnaire—that yes, they do bury their salad in half a cup of Hidden Valley Ranch, and they do choose white bread because 12-Grain Oroweat tastes like lightly sweetened wood chippings, and sometimes they even go a full three days where their only vegetable is ketchup? If food frequency questionnaires were hooked up to a polygraph, we might see some much different data (and some mysteriously disappearing respondents).
Another reference in our study du jour takes us to a validation report for the Nurses’ Health Study questionnaire. And here we find the same trend:
Mean daily amounts of each food calculated by the questionnaire and by the dietary record were also compared; the observed differences suggested that responses to the questionnaire tended to over-represent socially desirable foods.
Of course, if everyone over-reported or under-reported their food intake with the same magnitude of inaccuracy, we could still find some reliable associations between food questionnaires and health outcomes. But it turns out that how much someone fudges their food reporting—especially for specific menu items—varies wildly based on their personal characteristics. Using an Aussie-modified version of the Nurses’ Health Study questionnaire, a study from Australia measured how accurately people reported their food intake based on their gender, age, medical status, BMI, occupation, school-leaving age, and use of dietary supplements. Like with the other validation studies, it compared the results of the food frequency survey with the Almighty Weighed Food Record.
The surprising results? Folks with a “diagnosed medical condition”—including high cholesterol, high triglycerides, diabetes, high blood pressure, stroke, cancer, and heart disease—were much more likely to mis-report their meat consumption than folks without a diagnosed medical condition, generally overestimating their true intake on food frequency questionnaires compared to the weighed food record. Why this occurred is one of life’s great mysteries, but it might have something to do with the fact that people who develop diet- and lifestyle-related diseases pay less conscious attention to what they eat. (In this study, women were also more likely to inaccurately report their intake for a wide variety of foods—a phenomenon that’s been examined in greater depth by other researchers.)
So what does this mean for studies based on food frequency questionnaires, like the one currently hijacking the news outlets? Unfortunately for lovers of scientific accuracy, it means that meat consumption and modern diseases might be statistically more likely to show up hand-in-hand by mere fluke. If sick folks have a tendency—for whatever reason—to say they’re eating more meat than they really are, that’ll have profound effects on any diet-disease associations that turn up in observational studies, where correlations hinge so heavily on the accuracy of the data. And if the results of that Australian study are applicable not only in the Land Down Under but also in the Land Up Over, it could mean that meat is pretty much doomed to look guilty by association with disease whenever food frequency questionnaires are involved. Woe is meat!
Red-Meatophiles: A Species of Their Own
Now that our confidence in food frequency questionnaires should be thoroughly and disturbingly shattered, let’s hop back to the study in question. To gauge the effects of red meat consumption on mortality, the researchers for our Red Meat Consumption and Mortality study divided folks up into five quintiles based on their red meat intake. The first quintile represents the people who reported the fewest servings per day, while the fifth quintile represents the shameless red-meat gluttons who indulged in the most (or rather, reported indulging in the most). Luckily for us, the researchers provided a magical table of marvels comparing various diet and lifestyle variables between the quintiles. Please take a minute to look at it yourself and, if you feel so compelled, bask in its glory.
If you secretly suspected that this was a “people who eat red meat do a lot of unhealthy things that make them die sooner” study, you can now gloat.
Here are a few lifestyle variables I graph-ified for greater visual impact. (“Red Meat Intake” is measured in servings per day, and “Physical Activity” is measured in hours of metabolic equivalent tasks.)
As you can see, the folks eating the most red meat were also the least physically active, the most likely to smoke, and the least likely to take a multivitamin (among many other things you can spot directly in the table, including higher BMIs, higher alcohol intake, and a trend towards less healthy non-red-meat food choices). Although the researchers tried their darnedest to adjust for these confounders, not even fancy-pants math tricks can compensate for the immeasurable details involved in unhealthy living, the tendency for folks to misreport their diet and exercise habits, and whatever mild insanity emerges from trying to remember every food that hit your tongue during the past year.
And in case you didn’t spot them yet, our magical table has two particularly ogle-worthy things. The first one’s this:
If you had any doubt that people fib on food questionnaires, this should put your mind at ease. Take a look at the average (reported) calorie intake for the women in the first quintile of red meat consumption. Yes, that does say “1200 calories.” Yes, that is low enough to make most people wake themselves up at night as they unconsciously gnaw on their own arm in a quest for nourishment. And the red-meat-avoiding men aren’t much better, clocking in at a bit over 1600 calories for fully-grown adults. If there really is an 800-calorie gap between the folks with the lowest and highest red meat consumption, there’s obviously something much more significant going on in their diets than the color of their chosen animal foods. And if—in a much more likely scenario—there’s some major mis-reporting going on, that only bolsters the notion that we shouldn’t trust food frequency questionnaires any farther than we could throw ‘em.
SOURCE (See the original for graphics)
No comments:
Post a Comment