Research Notes: Nutrition

(08/16/07 - MedPage Today) Low-Fat Diet Not Good for Kids

Children need fat to fuel growth and should not be put on low-fat diets, researchers said. The findings of their small study support current Department of Agriculture guidelines recommending higher dietary fat intake for children than adults (25% to 35% of calories versus 20% to 35%), the investigators said.

The earlier version of those guidelines promoted a diet with less than 30% of calories from fat for children older than two, they noted. "This guideline was translated by some in an overzealous, but well-intentioned, manner to provide as little fat as possible in the diet leading to inadequate energy intake and compromised growth," they wrote.

To prevent interrupting children's growth, parents should keep kids' fat intake to a moderate level within the recommended range taking into account physical activity, the researchers suggested.

The report came just days after another research group recommended against low-calorie foods for children based on findings that diet products can distort how the young learn calorie-content cues and lead to overeating at meals. (See Low-Calorie Snacks May Not Help the Young Keep Pounds Off)

With the updated dietary guidelines in mind, the researchers studied fat oxidation of five men and five women ages 27 to 55 and the same number of boys and girls ages six to 10. All were healthy, of normal weight, and had a normal activity level without a rigorous physical training program. A consistent metabolic background was established for three days with a weight maintenance diet provided for participants as "take out." Then, each individual had metabolic rate measured over nine hours using a hood system or room calorimeter while they watched movies, read, or played games. Measurement was repeated on two separate occasions.

The researchers found that daily calorie expenditure during testing was as expected given the lack of physical activity: 2,072 kcal for men, 1,496 kcal for boys, 1,329 kcal for women, and 1,194 kcal for girls. However, energy expenditure normalized to lean body mass was significantly higher for children than adults (50.4 kcal/d/kg for boys, 52.4 for girls, 29.7 for men, and 29.48 for women, P<0.05). Likewise, total fat burned was not significantly different in adults than in children, even after correction for urea nitrogen excretion (51.4 g/24 hrs versus 62.7).

But, whole body fat oxidation was significantly greater in the children than in the adults, as reflected in lower mean respiratory quotients (0.84 versus 0.87, P<0.02). Children also burned more fat for the same energy expenditure (0.047 g/kcal/day versus 0.032, P<0.02).

Females at whatever age also burned more fat relative to calorie expenditure than males (0.052 g/kcal for girls and 0.042 for women versus 0.041 for boys and 0.023 for men, P=0.025).

Growth may be the reason kids burn more fat, the researchers surmised. "Prepubescent children may oxidize more fat relative to total energy expenditure than adults for the purpose of supporting normal growth processes such as higher rates of protein synthesis, lipid storage and bone growth," they wrote.

They dismissed the possibility that their findings could be chalked up to heightened fear or arousal among children during tests. "While not quantified, our subjective impression was that children were comfortable in the room calorimeter in a manner similar to the adults," the investigators wrote.

Nonetheless, the generalizability of the findings was limited by the small sample size, and larger studies would be needed to verify the results, they noted.

"Consistent with current dietary guidelines, a moderate-fat diet is appropriate for children within the context of a diet that meets their energy and nutrient needs," they concluded.

The study was supported by the National Dairy Council and the Penn State General Clinical Research Center through a grant from the National Institutes of Health. The researchers reported no conflicts of interest.

Reference: Kostyak JC, et al. Relative fat oxidation is higher in children than adults. Nutr J 2007.

Also: (08/16/07 - Daily Telegraph Australia) Low-fat foods a health risk for children, experts warn

Parents who cut out all fat from their children's diets are placing their health at risk, scientists have warned. Experts have long advised that a moderate intake of 'good' fats - such as olive and sunflower oils - is essential for proper growth and development, reports The Daily Mail. But concerns over the rise in obesity have prompted many families to adopt low-fat regimes.

Now researchers have shown that children burn more body fat than adults for each calorie spent, which means they get rid of it more easily. They hope this will convince parents not to go to extremes in their battle against the bulge.

The number of fat children has doubled in ten years, with one in four children aged 11-15 now classified as obese - so fat it threatens their health. The Government is widely expected to miss its target to halt the rise in childhood obesity among under-11s by 2010.

Cutting out all fat is not the solution, however, according to the US researchers writing in the online Nutrition Journal. Dr John Kostyak and a team from the Pennsylvania State University measured the rate at which whole body fat was used up in ten children aged six to ten, and ten adults. All were in the healthy, middle range of weight classification for their age and sex. All the volunteers were given the same typical American diet for three days prior to testing, although adults had larger portions.

The volunteers spent nine hours on three separate days at a low physical activity level, watching movies or reading. They were tested in a room equipped as a calorimeter - a system to measure heat produced by the body as energy - or under a hood system, to calculate oxygen and carbon dioxide gas levels. The team also measured the amount of nitrogen in the subjects' urine, and used this to calculate how much fat they oxidised.

The absolute amount of fat burned in a day was similar for both children and adults. But children burned considerably more fat relative to the amount of energy they used.

The researchers calculated the grams of fat oxidised per calorie of energy expenditure and found it was around 50 per cent higher. Women and girls used fat at a higher rate than men and boys of a comparable age.

Other studies have shown that dietary fat helps normal growth and includes fat-soluble vitamins vital for the development of eyesight and other organs.

Dr Kostyak said: "Sufficient fat must be included in the diet for children to support normal growth and development."

Jacqui Lowdon, of the British Dietetic Association, said parents needed reminding that fat was good for children - providing it was the right kind. She said: "Children need the fatty acids and omega 3 found in fat, and fat soluble vitamins A,D and E for growth, development and eyesight. There is a risk parents could think that all fat is bad for their children - some years ago we had a phenomenon known as Muesli Belt syndrome where parents went to extremes with food that didn't contain all the nutrients they need."

She said 35 per cent of calories from a healthy diet should come from fat, ideally polyunsaturated and mono-unsaturated fats such as olive and sunflower oils. "These set up healthy eating patterns for life" she added.

(06/23/07 - Science News) Concerns over Genistein - The heart of the issue

For the past few decades, health magazines - and, more recently, health Web sites - have touted the virtues of soy. Some studies have suggested it can dramatically cut heart risks. Others describe this legume as a potentially powerful weapon against cancer. Soy beans - and the tofu, tempeh, snack "nuts," and other products made from them - have risen to become media superstars.

Consumers, however, have been somewhat slow to embrace soy products as dietary staples. One new study suggests that might be a good thing, at least for older women.

A woman's risk of developing heart disease climbs at menopause, when her body's production of estrogens wanes. Augmenting these diminishing sex hormones - in part, to protect the heart - has been one rationale for treating post-menopausal women with hormone-replacement therapy. However, because of risks associated with this therapy physicians have been reluctant to prescribe these powerful hormones during the past decade.

Many plants, including soy, contain natural mimics of estrogen. Some scientists have reasoned that supplementing the diet with these plant-derived isoflavones, which include genistein, daidzein, equol, and glycitein, might also protect the heart.

That notion has made its way into the popular literature and fueled the marketing of isoflavone-rich soy products as natural, healthful alternatives to hormone-replacement therapy. Medical evidence of their benefits, however, has been weak at best, notes Carl J. Pepine, chief of cardiology at the University of Florida College of Medicine in Gainesville.

So, he and researchers from five other medical institutions decided to investigate whether women who have high concentrations of genistein in their blood—indicative of higher dietary intakes of "estrogens" from soy and other plants - would have better vascular health. They tested that hypothesis in women who had recurrent chest pain, which is a symptom of incipient heart disease.

The opposite of their hypothesis proved true, they now report in the May Journal of Women's Health. High genistein levels correlated with poor cardiovascular health.

"There are a lot of women taking these things [isoflavone-rich products], without any direct evidence that they're beneficial," Pepine notes. The new study, he says, adds to a small but growing body of research suggesting there could be a down side to overindulging in them.

Pepine's group evaluated the role of plant estrogens among participants of the Women's Ischemia Syndrome Evaluation (WISE) project. Funded by the National Institutes of Health and begun more than a decade ago, WISE has recruited more than 900 women to investigate whether heart disease tends to develop differently in them than it does in men.

There's reason to suspect that it might: Several studies have shown that most women who experience recurrent chest pain don't have evidence of obstructed vessels to the extent that men do. It could be that the obstructions are merely harder for doctors to spot in women, for some reason. But it's also possible that women develop a different type of vascular disease. For instance, small vessels may not adjust their diameters, from moment to moment, as readily as they do in men. Such constant vascular responsiveness is essential to meeting the varying oxygen needs of tissues.

Women participating in the WISE project do show far less obstruction of the coronary arteries than is typical of men with heart disease, as has been found in other studies. Moreover, women in this study - and several others - have shown less vascular responsiveness than is typical in men with cardiovascular disease.

In addition to testing vascular responsiveness in the women, the WISE project has been exploring the role of natural sex hormones and their mimics - like soy's plant estrogens - in the development of heart disease and its manifestations.

In the new study, the researchers correlated blood concentrations of genistein against various measures of vascular responsiveness in 106 WISE participants, all women around the age of 55. Imaging tests revealed that only 24 percent of these women had obstructive heart disease. However, all of the women had reduced blood flow, a symptom of heart disease. Those whose vessels were least able to relax, dilate, and increase flow rate in response to changing physiological needs tended to have the highest blood concentrations of genistein.

Ordinarily, Pepine explains, a vessel should be able to dilate enough to triple or even quadruple its normal rate of blood flow. This permits substantially greater oxygenation of tissues fed by that vessel. However, in the new WISE analysis, women with the poorest vascular responsiveness couldn't even double blood flow within small vessels. As a woman's blood concentrations of genistein fell, however, the ability of those coronary microvessels to dilate increased. Some were able to triple their flow rates.

What's happening?

Blood vessels have different layers. The interior one, which is in contact with the blood, is known as the endothelium. In response to changes in blood flow and blood pressure, its cells can release chemicals - principally nitric oxide - that can penetrate into the vessel wall and relax smooth-muscle cells that make up the middle vessel layer. The tension or relaxation of these muscle cells controls a vessel's diameter and blood-flow rate.

Some problems in vascular responsiveness trace to the endothelium. Other problems can stem from damage to the smooth-muscle cells themselves. In the new study, Pepine's group investigated both systems.

Pepine had expected the epithelium, which comes into direct contact with plant estrogens in the blood, to prove more sensitive to genistein concentrations. In fact, both vessel layers appeared sensitive, Pepine told Science News Online, although "we saw the biggest effect at the muscle-cell level. That was definitely a surprise."

One possibility, he says, is that plant estrogens block chemical receptors on smooth-muscle cells that recognize adenosine. That compound, a byproduct of chemicals released by the heart, is believed to play a pivotal role in vessel dilation, he explains.

If that is indeed the problem, he says, then reducing exposure to these plant estrogens may improve small-vessel responsiveness.

Currently, the WISE investigators can't point to soy specifically as the source of the genistein measured in the studied women because the researchers didn't obtain detailed dietary histories before the participants were tested. It's not that the scientists weren't interested, Pepine says, but a matter of expediency. Participants of the complex study completed many tests and questionnaires. In fact, the one probing characteristics of a woman's chest pains was itself 12 pages long. Asking for detailed dietary information just seemed to be too much of an imposition on the study's volunteers, he says.

However, dietary sources of plant estrogens are something his team plans to investigate in the future. The researchers also plan to randomly assign some women to diets enriched with genistein, and others to meals low in it. That's the only way to tell whether such plant estrogens actually impair vascular responsiveness. It could rule out the possibility that WISE volunteers who experienced the most discomfort due to vascular unresponsiveness were those most driven to find an over-the-counter remedy - like soy foods or food supplements containing soy isoflavones.

Food Chem Toxicol. 2006 Jan.
Acute, subchronic and chronic safety studies with genistein in rats.
Michael McClain R, Wolz E, Davidovich A, Pfannkuch F, Edwards JA, Bausch J.
McClain Associates, Randolph, NJ, USA.
Genistein is a phytoestrogen that occurs naturally in the diet, especially in soy based foods. There is wide spread interest in phytoestrogens as chemopreventive agents for a variety of diseases and cancers based on epidemiologic evidence. Although soy, and its constituents such as genistein, have been consumed at high levels in several Asian populations without apparent adverse effects, concern has been raised about potential adverse effects due to the estrogenic and other activities. Safety studies with genistein were conducted in the Wistar rat including two acute studies, two subchronic (4 weeks and 13 weeks) and a chronic 52-week dietary admix study. In the acute studies, genistein had a low order of toxicity. In the three repeated dose safety studies at doses up to 500 mg/kg/day, genistein was well tolerated. In all of the studies, decreased food consumption and body weight gain were observed at 500 mg/kg/day. The main hematological findings were decreased red blood cell parameters at 500 mg/kg/day with a compensatory increase in reticulocytes. For clinical chemistry, with the exception of a slight increase in gamma glutamyl transferase in male and female rats at the high dose, there were a number of other minor changes considered not toxicologically significant. At necropsy, there were relatively few macroscopic changes; in the 52-week study, dilation of the uterus with fluid at the high dose and cysts of the ovaries in treated animals were observed. Organ weight changes in male rats at the high dose of 500 mg/kg/day included increased kidney, spleen, adrenal and testes weights and for females included, increased liver, kidney, spleen, ovary and uterus weights. After 4 and 13 weeks of treatment with genistein, there were no treatment related histopathologic findings. After 26 and 52 weeks of treatment, histological changes were seen in the female reproductive organs (ovaries and uterus), and in males (epididymides and prostate), and bone, kidneys, heart, liver and spleen in both sexes. After 52 weeks of treatment of males, vacuolation of the epididymal epithelium at 500 mg/kg/day and inflammation of the prostate were recorded at a higher incidence at 50 and 500 mg/kg/day. In females, cytological changes in the uterus, squamous metaplasia at 50 and 500 mg/kg/day and hyperplasia at 500 mg/kg/day were observed. Furthermore, hydrometra of the uterus and findings in the vagina consisting of anestric or diestrus vaginal mucosa with vaginal mucification, hyperplastic epithelium and multifocal cystic degeneration were noted at 500 mg/kg/day. Atrophy of the ovaries increased in severity in animals at 50 and 500 mg/kg/day. Osteopetrosis (hyperostosis) was observed in male and female rats at 50 and 500 mg/kg/day along with a compensatory increase in extramedullary hemopoiesis in the spleen; females were more affected than males. Hepatocellular hypertrophy and minimal bile duct proliferation were recorded at a higher incidence in animals at 500 mg/kg/day. It is concluded that almost all of the treatment related findings in these studies are related to the estrogenic properties of genistein as a phytoestrogen and would be expected to occur with a compound with estrogenic activity. The hormonally related changes were considered to be functional in nature and thus not adverse effects. Most of the findings in these studies were limited to the high dose of 500 mg/kg/day and were reversible. The few findings observed at 50 mg/kg/day were relatively minor and in view of the functional (hormonally mediated) nature of the effects, were considered not adverse effects. The increased incidence of minimal bile duct proliferation and slightly increased gamma glutamyl transferase are indicative of a mild hepatic effect at the high dose of 500 mg/kg/day. The no observed adverse effect level (NOAEL) of genistein is considered to be 50 mg/kg/day based on the presence of mild hepatic effects at the high dose of 500 mg/kg/day. The no observed effect level (NOEL) is considered to be 5 mg/kg/day based on the hormonally induced functional changes at higher doses.