High-fat, low-carb foods are a popular choice for dieters, but new laboratory research by University of Alabama at Birmingham cardiologists indicates these may be detrimental to the health of people who have ischemic cardiovascular disease or a predisposition to heart attacks.
UAB cardiologist Steven Lloyd, M.D., Ph.D., will present the animal-model studies in four moderated poster sessions during the 2012 American College of Cardiology Scientific Sessions Sunday, March 25, 2012, in Chicago.
“Obesity and heart disease are major public health issues and are the leading causes of other disease — including diabetes, stroke and death,” Lloyd says. “Many overweight people turn to a high-fat, low-carb diet because of its effectiveness; but research has yet to adequately assess safety, and there is insufficient evidence to recommend them for people seeking to lose weight.”
Lloyd and colleagues first published in Life Sciences in 2008 that high-fat, low-carb diets affect the types of fuel the heart uses to function, alter insulin-signaling following a heart attack and increase post-heart-attack damage in normal-weight rats.
In this latest research, the team tested to learn if those findings would hold steadfast among obese rats and rats with heart disease.
“Overall, we found that obese rats fed a high-fat, low-carb diet — comparable to that humans would consume — had larger, more damaging and deadly heart attacks than rats fed the control diet,” Lloyd says. “Our findings also suggest that, at the cellular level, a high-fat, low-carb diet impaired recovery of heart function in obese rats immediately following a heart attack.”
Lloyd says that four studies are not definitive enough to say high-fat, low-carb diets are harmful or beneficial, but they do present enough preliminary evidence of harm to warrant further investigation.
“These findings tell us that for those who are trying to lose weight, if you have coronary artery disease or if for some reason you are at greater risk of having a heart attack, a high-fat, low-carb diet might not be a good thing for you,” Lloyd says.
The four presentations by Lloyd each answer different but connected questions:
• What is the effect of high-fat, low-carb diets on the size of a heart attack, and how well does the heart recovers after a cardiac event?
• What is the impact of high-fat, low-carb diets on heart attack size and survival in the immediate aftermath of a heart attack?
• What is the effect of high-fat, low-carb diets on mitochondrial function and oxidative stress in the heart, and how these affect tissue damage from reduced blood flow to the heart during an attack?
• How do high-fat, low-carb diets affect the heart’s insulin sensitivity and the fuels it uses to function during both normal function and during a heart attack?
Heart attack size and heart recovery
Lloyd and his colleagues fed obese rats either a control diet — which was a low-fat diet — or a high-fat, low-carb diet. The outcome for the obese rats was the same as described in normal-weight rats the 2008 — that type of diet leads to greater injury to the heart muscle and reduced functional recovery.
“Rat size did not matter,” Lloyd says. “The heart attacks in the obese rats — as in the normal weight rats — were much larger in those that ate a high-fat, low-carb diet and recovery of function was much better in those that ate the control diet than in those that at the high-fat, low-carb diet.”
Heart attack size and survival
Lloyd and his colleagues found that rats fed a high-fat, low-carb diet had greater damage to the heart muscle from a heart attack and were at greater risk of death from pump failure and arrhythmias when compared to the rats fed the control diet.
“The majority of the rats on the high-fat, low-carb diet didn’t survive the initial attack; among those that did survive, the attack size was considerably larger than among rats fed the control diet,” Lloyd says. “And many rats that died during the attack did so because of an arrhythmia. This could be attributed to the size of the attack.”
Oxidative stress
Lloyd says research has shown that oxidative stress during heart attacks plays a role in activating different chemical processes that cause cell death during and after blood flow is restricted to the heart. These chemical processes can last for a few hours or days after normal blood flow returns and be extremely damaging to the heart muscle.
Previous research also has linked high-fat diets to oxidative stress in the brain, causing cognitive impairment, and in the liver, causing fatty liver disease. Lloyd and his colleagues wanted to assess the affect of a high-fat, low-carb diet on mitochondrial function and oxidative stress in the heart and its subsequent affect on tissue during a heart attack.
“Obese rats fed the high-fat, low-carb diet had significantly larger heart attacks than those fed the control diet and had much more difficulty recovering function after blood flow was restored to the heart,” Lloyd says. “This might be partly due to a loss in the number of mitochondria in heart muscle cells, and an increase in formation of proteins that led to high oxidant stress, and a decrease in proteins that reduce oxidant stress. We found that all of these factors occur in rats fed the high-fat, low-carb diet. This could definitely be contributing to the harmful process of a heart attack.”
Insulin sensitivity
The primary fuel for the body is carbohydrates broken down into glucose. Once glucose is created, insulin then causes cells in muscle and other tissues to take up glucose from the blood and use it for energy. When someone eats a high-fat, low-carb diet, the body — including the heart — turns to fat as its next source of fuel. Ketones are molecules generated during fat metabolism. Lloyd says though research has shown the heart muscle can use many sources of fuel for energy, not all of them are as efficient. Glucose, or carbohydrates, tend to be the most efficient fuel when the heart is trying to recover from a damaging event.
“We found that a high-fat, low-carb diet impaired cardiac tissue response to insulin, which is known to be important in protecting the heart immediately after a heart attack, as it helps limit the size of a heart attack and protects muscle tissue,” Lloyd says. “We also found that, while the heart easily uses more ketones to function under normal conditions when the rats were fed a high-fat, low-carb diet, following a heart attack it uses less ketones. While it is unclear why this happens, without utilizing the most efficient fuel — carbohydrates — to the fullest extent, the heart is less efficient at recovering function.”
Lloyd says by no means does this research say no one should be on a high-fat, low-carb diet. In fact, these diets have been shown to improve certain markers in cholesterol profiles and they do help people lose weight. What it does say, he says, is that much more investigation is needed into the benefits and risks of a high-fat, low-carb diet.
“Right now, if I were considering a high-fat, low-carb diet, I would ask myself if the benefits outweigh the heart-attack issues this research has revealed,” he says. “If I had heart disease or I was predisposed to having a heart attack, I would think carefully before starting this type of diet.”
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Monday, March 26, 2012
Thursday, March 22, 2012
The Smell of Food Affects How Much You Eat
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Bite size depends on the familiarly and texture of food. Smaller bite sizes are taken for foods which need more chewing and smaller bite sizes are often linked to a sensation of feeling fuller sooner. New research published in BioMed Central's new open access journal Flavour, shows that strong aromas lead to smaller bite sizes and suggests that aroma may be used as a means to control portion size.
The aroma experience of food is linked to its constituents and texture, but also to bite size. Smaller bites sizes are linked towards a lower flavour release which may explain why we take smaller bites of unfamiliar or disliked foods. In order to separate the effect of aroma on bite size from other food-related sensations researchers from the Netherlands developed a system where a custard-like dessert was eaten while different scents were simultaneously presented directly to the participants nose.
The results showed that the stronger the smell the smaller the bite. Dr Rene A de Wijk, who led the study, explained, "Our human test subjects were able to control how much dessert was fed to them by pushing a button. Bite size was associated with the aroma presented for that bite and also for subsequent bites (especially for the second to last bite). Perhaps, in keeping with the idea that smaller bites are associated with lower flavour sensations from the food and that, there is an unconscious feedback loop using bite size to regulate the amount of flavour experienced."
This study suggests that manipulating the odour of food could result in a 5-10% decrease in intake per bite. Combining aroma control with portion control could fool the body into thinking it was full with a smaller amount of food and aid weight loss.
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Bite size depends on the familiarly and texture of food. Smaller bite sizes are taken for foods which need more chewing and smaller bite sizes are often linked to a sensation of feeling fuller sooner. New research published in BioMed Central's new open access journal Flavour, shows that strong aromas lead to smaller bite sizes and suggests that aroma may be used as a means to control portion size.
The aroma experience of food is linked to its constituents and texture, but also to bite size. Smaller bites sizes are linked towards a lower flavour release which may explain why we take smaller bites of unfamiliar or disliked foods. In order to separate the effect of aroma on bite size from other food-related sensations researchers from the Netherlands developed a system where a custard-like dessert was eaten while different scents were simultaneously presented directly to the participants nose.
The results showed that the stronger the smell the smaller the bite. Dr Rene A de Wijk, who led the study, explained, "Our human test subjects were able to control how much dessert was fed to them by pushing a button. Bite size was associated with the aroma presented for that bite and also for subsequent bites (especially for the second to last bite). Perhaps, in keeping with the idea that smaller bites are associated with lower flavour sensations from the food and that, there is an unconscious feedback loop using bite size to regulate the amount of flavour experienced."
This study suggests that manipulating the odour of food could result in a 5-10% decrease in intake per bite. Combining aroma control with portion control could fool the body into thinking it was full with a smaller amount of food and aid weight loss.
Ω
Tuesday, March 6, 2012
STUDY: MOST WEIGHT LOSS SUPPLEMENTS ARE NOT EFFECTIVE
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An Oregon State University researcher has reviewed the body of evidence around weight loss supplements and has bad news for those trying to find a magic pill to lose weight and keep it off – it doesn’t exist.
Melinda Manore reviewed the evidence surrounding hundreds of weight loss supplements, a $2.4 billion industry in the United States, and said no research evidence exists that any single product results in significant weight loss – and many have detrimental health benefits.
The study is online in the International Journal of Sport Nutrition and Exercise Metabolism.
A few products, including green tea, fiber and low-fat dairy supplements, can have a modest weight loss benefit of 3-4 pounds (2 kilos), but it is important to know that 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,” Manore said.
Manore looked at supplements that fell into four categories: products such as chitosan that block absorption of fat or carbohydrates, stimulants such as caffeine or ephedra that increase metabolism, products such as conjugated linoleic acid that claim to change the body composition by decreasing fat, and appetite suppressants such as soluble fibers.
She found that many products had no randomized clinical trials examining their effectiveness, and most of the research studies did not include exercise. Most of the products showed less than a two-pound weight loss benefit compared to the placebo groups.
“I don’t know how you eliminate exercise from the equation,” Manore said. “The data is very strong that exercise is crucial to not only losing weight and preserving muscle mass, but keeping the weight off.”
Manore, professor of nutrition and exercise sciences at OSU, is on the Science Board for the President’s Council on Fitness, Sports and Nutrition. Her research is focused on the interaction of nutrition and exercise on health and performance.
“What people want is to lose weight and maintain or increase lean tissue mass,” 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.”
As a dietician and researcher, Manore 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. Depending on the individual, increasing protein may be beneficial (especially for those trying to not lose lean tissue), but the only way to lose weight is to make a lifestyle change.
“Adding fiber, calcium, protein and drinking green tea can help,” Manore said. “But none of these will have much effect unless you exercise and eat fruits and vegetables.”
Manore’s general guidelines for a healthy lifestyle include:
- Do not leave the house in the morning without having a plan for dinner. Spontaneous eating often results in poorer food choices.
- If you do eat out, start your meal with a large salad with low-calorie dressing or a broth-based soup. You will feel much fuller and are less likely to eat your entire entrée. Better yet: split your entrée with a dining companion or just order an appetizer in addition to your soup or salad.
- Find ways to keep moving, especially if you have a sedentary job. Manore said she tries to put calls on speaker phone so she can walk around while talking. During long meetings, ask if you can stand or pace for periods so you don’t remain seated the entire time
- Put vegetables into every meal possible. Shred vegetables into your pasta sauce, add them into meat or just buy lots of bags of fruits/vegetables for on-the-go eating.
- Increase your fiber. Most Americans don’t get nearly enough fiber. When possible, eat “wet” sources of fiber rather than dry – cooked oatmeal makes you feel fuller than a fiber cracker.
- Make sure to eat whole fruits and vegetables instead of drinking your calories. Eat an apple rather than drink apple juice. Look at items that seem similar and eat the one that physically takes up more space. For example, eating 100 calories of grapes rather than 100 calories of raisins will make you feel fuller.
- Eliminate processed foods. Manore said research increasingly shows that foods that are harder to digest (such as high fiber foods) have a greater “thermic effect” – or the way to boost your metabolism.
An Oregon State University researcher has reviewed the body of evidence around weight loss supplements and has bad news for those trying to find a magic pill to lose weight and keep it off – it doesn’t exist.
Melinda Manore reviewed the evidence surrounding hundreds of weight loss supplements, a $2.4 billion industry in the United States, and said no research evidence exists that any single product results in significant weight loss – and many have detrimental health benefits.
The study is online in the International Journal of Sport Nutrition and Exercise Metabolism.
A few products, including green tea, fiber and low-fat dairy supplements, can have a modest weight loss benefit of 3-4 pounds (2 kilos), but it is important to know that 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,” Manore said.
Manore looked at supplements that fell into four categories: products such as chitosan that block absorption of fat or carbohydrates, stimulants such as caffeine or ephedra that increase metabolism, products such as conjugated linoleic acid that claim to change the body composition by decreasing fat, and appetite suppressants such as soluble fibers.
She found that many products had no randomized clinical trials examining their effectiveness, and most of the research studies did not include exercise. Most of the products showed less than a two-pound weight loss benefit compared to the placebo groups.
“I don’t know how you eliminate exercise from the equation,” Manore said. “The data is very strong that exercise is crucial to not only losing weight and preserving muscle mass, but keeping the weight off.”
Manore, professor of nutrition and exercise sciences at OSU, is on the Science Board for the President’s Council on Fitness, Sports and Nutrition. Her research is focused on the interaction of nutrition and exercise on health and performance.
“What people want is to lose weight and maintain or increase lean tissue mass,” 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.”
As a dietician and researcher, Manore 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. Depending on the individual, increasing protein may be beneficial (especially for those trying to not lose lean tissue), but the only way to lose weight is to make a lifestyle change.
“Adding fiber, calcium, protein and drinking green tea can help,” Manore said. “But none of these will have much effect unless you exercise and eat fruits and vegetables.”
Manore’s general guidelines for a healthy lifestyle include:
- Do not leave the house in the morning without having a plan for dinner. Spontaneous eating often results in poorer food choices.
- If you do eat out, start your meal with a large salad with low-calorie dressing or a broth-based soup. You will feel much fuller and are less likely to eat your entire entrée. Better yet: split your entrée with a dining companion or just order an appetizer in addition to your soup or salad.
- Find ways to keep moving, especially if you have a sedentary job. Manore said she tries to put calls on speaker phone so she can walk around while talking. During long meetings, ask if you can stand or pace for periods so you don’t remain seated the entire time
- Put vegetables into every meal possible. Shred vegetables into your pasta sauce, add them into meat or just buy lots of bags of fruits/vegetables for on-the-go eating.
- Increase your fiber. Most Americans don’t get nearly enough fiber. When possible, eat “wet” sources of fiber rather than dry – cooked oatmeal makes you feel fuller than a fiber cracker.
- Make sure to eat whole fruits and vegetables instead of drinking your calories. Eat an apple rather than drink apple juice. Look at items that seem similar and eat the one that physically takes up more space. For example, eating 100 calories of grapes rather than 100 calories of raisins will make you feel fuller.
- Eliminate processed foods. Manore said research increasingly shows that foods that are harder to digest (such as high fiber foods) have a greater “thermic effect” – or the way to boost your metabolism.
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