*Low fat foods reduce testosterone levels in men, researchers find
*High protein meals boost heart attack, lead to weight loss, say study
*Mediterranean, fasting, Paleo menus induce health improvements
Data suggest that those who follow healthful low fat and low carb diets have a lower overall death risk.A large new study has examined the link between diet type and total mortality.
Dr. Zhilei Shan from the Harvard T. H. Chan School of Public Health in Boston, MA, United States (U.S.) and colleagues in their new study paper wrote: “Diet plays an important role in […] public health, and suboptimal diet is estimated as the first leading cause of death and the third leading cause of disability-adjusted life-years lost in the U.S.”
Their findings now appear in the journal JAMA Internal Medicine.In their research, Shan and team analysed the data of more than 37,000 people to determine whether or not there were any associations between different diet types and mortality.
More specifically, the investigators wanted to find out if different types of low fat and low carb diet are associated with total mortality. Although there have been several studies into the links between diet and death risk, the researchers note that — to their knowledge — none have looked specifically at how low carb and low fat diets of different qualities may fit into the equation.
“Consumption of carbohydrates from refined grains and added sugars has been adversely associated with health outcomes, whereas consumption of carbohydrates from whole grains, non-starchy vegetables, and whole fruits appears to be beneficial,” explain the study authors.
“Likewise,” they say, “replacing saturated fat with unsaturated fat was associated with lower risk of heart disease and mortality.”For these reasons, the investigators thought it was important to identify and emphasize any associations between different diet types, different quality diets, and mortality risk.
For their study, the researchers analyzed the data of 37,233 U.S. adults with a mean age of 49.7 years. The data came from eight cycles of the National Health and Nutrition Examination Survey (NHANES), from 1999 to 2014.In total, the follow-up period accounted for 297,768 person years. This refers to the amount of follow-up time for all the participants included in the NHANES surveys.
During this time, the researchers recorded a total of 4,866 deaths; of which 849 were related to heart disease and 1,068 were related to cancer.Using the NHANES reports regarding people’s macronutrient consumption, the researchers were able to infer different diet quality types.
The team found no association between overall low carb and low fat diet scores and total mortality risk.However, they did find an association between unhealthful low carb and low fat diet scores — indicating adherence to poor quality low fat and low carb diets — and a higher total mortality risk.On the other hand, better quality low fat and low carb diets were associated with a lower total mortality risk.
The researchers also report that “participants with a higher overall low carb dirt score score” — indicative of a poorer quality diet — “were more likely to be older and non-Hispanic white, to have higher body mass index, educational level, income level, and cholesterol intake, and to have lower total energy intake.”
As for those with higher low fat diet scores, the investigators point out that they tended to be part of an ethnic minority group, to not smoke, to have lower weights, and to have lower cholesterol levels.When trying to find an explanation for the association between different diet quality types and mortality risk, Shan and colleagues point out that many biological mechanisms could play a role.
They wrote, “Fat provides more than twice as much energy as carbohydrates and protein by weight. A high saturated fat diet is highly palatable and may lead to overconsumption and obesity.”“Low quality carbohydrates, such as refined grains and added sugars, provide limited nutritional value, and their high glycemic load could be associated with high postprandial glucose and insulin, inflammation, insulin resistance, and dyslipidemia.”
Although the researchers emphasise that the main strength of their study was the sheer size of the population sample — as well as the lengthy follow-up time for data collection — they also caution that the research had a number of limitations.These include the fact that they could not identify which specific versions of the various low carb and low fat diets each participant had followed.
This means, in the study authors’ words, “The results could not be directly translated to the assessment of health benefit or risk associated with the popular versions of the diets.”They also note that the participants self-reported the data regarding their diets, which means that they may not be entirely accurate. The team was also unable to verify whether or not the relationship between diet quality and mortality risk was of a causal nature.
Also, a new study finds that low-fat diets slightly reduce levels of serum testosterone in men. At this stage, it is unclear whether the differences are clinically meaningful. Testosterone deficiency occurs when a male’s body does not produce enough serum testosterone. Though exercise and weight loss can combat this deficiency, a study published in The Journal of Urology suggests that the type of diet matters.
The new study finds that men following a low-fat diet may have lower serum testosterone levels than those with different diets.Scientists have linked a deficiency of this hormone to a variety of health issues, including: reduced bone mass; erectile dysfunction; diminished energy and sex drive; sleeping difficulties; mood swings; reduced semen; increased body fat; hair loss; hot flashes; reduced testicle size; and changes in cognition.
In addition, there is evidence of a possible connection between low testosterone and chronic conditions such as high blood pressure and type 2 diabetes. Low serum testosterone levels may also contribute to certain aggressive types of cancer.While in some cases the deficiency results from an identifiable cause, its source often remains unknown.
While weight reduction can lead to an increase in testosterone levels, in some cases it has the opposite effect. Precisely why losing weight can help resolve low serum testosterone is unclear.Hoping to shed light on this issue, the researchers behind the recent study have investigated the potential influence of fat intake on testosterone. They write: “While dieting for weight loss will clearly help optimize cardiovascular health, with corresponding reductions in lipid profiles, the effect of diet on [testosterone] is not well established.”
The authors of the study began with the intention of assessing the effects of four diets on testosterone: a low-fat diet, as defined by the American Heart Association (AHA); a Mediterranean diet, which involves a high intake of fruits, vegetables, and whole grains and a minimal intake of animal protein and dairy products, and thus animal fats; a low-carbohydrate diet, as defined by the AHA; and a nonrestrictive diet.The researchers analyzed data sets from the National Health and Nutrition Examination Survey. The relevant data had been collected during three periods: 1999–2000, 2003–2004, and 2011–2012. For the survey, men aged 18–80 had submitted a 2-day dietary history and undergone serum testosterone testing.
Overall, the researchers analyzed data from 3,128 men. While 457 men from this group had followed a low-fat diet and 764 had followed a Mediterranean diet, only two had followed a low-carbohydrate diet. The researchers therefore excluded this diet from their analysis.“We found that men who adhered to a fat-restrictive diet had lower serum testosterone than men on a nonrestrictive diet,” says lead author Dr. Jake Fantus, of the University of Chicago Medical Center, in Illinois.
The mean serum testosterone level for the entire cohort was roughly 435.5 nanogrammes per deciliter (ng/dl). Men on a low-fat diet had an average serum testosterone level of 411 ng/dl, and those on a Mediterranean diet had an average of 413 ng/dl.
After adjusting for factors that can influence testosterone, such as age, physical activity, and body mass index, the researchers determined that the Mediterranean diet did not cause a significant reduction in testosterone, whereas the reduction associated with a low-fat diet was small but significant.The study admits, “The clinical significance of small differences in serum [testosterone] across diets is unclear,” and acknowledges “Future prospective research is required to corroborate these findings and elucidate the mechanisms by which restrictive dieting may affect serum [testosterone].”
Meanwhile, the implications of the study’s findings may vary depending on other health indicators.The authors conclude that men with obesity may view a potential slight reduction in serum testosterone to be a relatively minor consideration in comparison with the potential benefits of a low-fat diet.Men with a testosterone deficiency who are maintaining a healthy weight, however, may wish to consider an alternate diet, if the findings of the current study are supported by more research.
Also, high-protein diets may help people lose weight and build muscle, but a new study in mice suggests they have a down side: They lead to more plaque in the arteries. Further, the new research shows that high-protein diets spur unstable plaque — the kind most prone to rupturing and causing blocked arteries. More plaque buildup in the arteries, particularly if it’s unstable, increases the risk of heart attack.
The new study, by researchers at Washington University School of Medicine in St. Louis, appears January 23 in the journal Nature Metabolism.“There are clear weight-loss benefits to high-protein diets, which has boosted their popularity in recent years,” said senior author Babak Razani, MD, PhD, an associate professor of medicine. “But animal studies and some large epidemiological studies in people have linked high dietary protein to cardiovascular problems. We decided to take a look at whether there is truly a causal link between high dietary protein and poorer cardiovascular health.”
The researchers studied mice fed a high-fat diet to deliberately induce atherosclerosis, or plaque buildup in the arteries. According to Razani, mice must eat a high-fat diet to develop arterial plaque. Therefore, some of the mice received a high-fat diet that was also high in protein. And others were fed a high-fat, low-protein diet for comparison.
“A couple of scoops of protein powder in a milkshake or a smoothie adds something like 40 grams of protein — almost equivalent to the daily recommended intake,” Razani said. “To see if protein has an effect on cardiovascular health, we tripled the amount of protein that the mice receive in the high-fat, high-protein diet — keeping the fat constant. Protein went from 15% to 46 per cent of calories for these mice.”
The mice on the high-fat, high-protein diet developed worse atherosclerosis — about 30 per cent more plaque in the arteries — than mice on the high fat, normal-protein diet, despite the fact that the mice eating more protein did not gain weight, unlike the mice on the high fat, normal-protein diet.“This study is not the first to show a telltale increase in plaque with high-protein diets, but it offers a deeper understanding of the impact of high protein with the detailed analysis of the plaques,” Razani said. “In other words, our study shows how and why dietary protein leads to the development of unstable plaques.”
Plaque contains a mix of fat, cholesterol, and calcium deposits and dead cells. Past work by Razani’s team and other groups has shown that immune cells called macrophages work to clean up plaque in arteries. But the environment inside plaque can overwhelm these cells, and when such cells die, they make the problem worse, contributing to plaque buildup and increasing plaque complexity.
“In mice on the high-protein diet, their plaques were a macrophage graveyard,” Razani said. “Many dead cells in the core of the plaque make it extremely unstable and prone to rupture. As blood flows past the plaque, that force — especially in the context of high blood pressure — puts a lot of stress on it. This situation is a recipe for a heart attack.”
To understand how high dietary protein might increase plaque complexity, Razani and his colleagues studied the path protein takes after it has been digested — broken down into its original building blocks, called amino acids. Razani and his team found that excess amino acids from a high-protein diet activate a protein in macrophages called mTOR, which tells the cell to grow rather than go about its housecleaning tasks. The signals from mTOR shut down the cells’ ability to clean up the toxic waste of the plaque, and this sets off a chain of events that results in macrophage death. The researchers found that certain amino acids, especially leucine and arginine, were more potent in activating mTOR — and derailing macrophages from their cleanup duties, leading to cell death — than other amino acids.
“Leucine is particularly high in red meat, compared with, say, fish or plant sources of protein,” Razani said. “A future study might look at high-protein diets with different amino acid contents to see if that could have an effect on plaque complexity. Cell death is the key feature of plaque instability. If you could stop these cells from dying, you might not make the plaque smaller, but you would reduce its instability.
“This work not only defines the critical processes underlying the cardiovascular risks of dietary protein but also lays the groundwork for targeting these pathways in treating heart disease,” he said.
Also, new University of Otago research shows there were some weight loss and health benefits for overweight adults who followed the Mediterranean, Intermittent Fasting and Paleo diets, though adherence to the diets dropped off considerably during the one-year study.Intermittent fasting — whereby participants limit their energy intake to about 25 per cent of their usual diet (500kcal for women and 600kcal for men) on two self-selected days per week, led to slightly more weight loss than the other diets. The Mediterranean diet also improved blood sugar levels.
Co-lead author Dr. Melyssa Roy, a Research Fellow in the Department of Medicine, says the amount of weight loss was modest — on average two to four kilograms for the 250 participants, but for those choosing the fasting or Mediterranean diets, clinically significant improvements in blood pressure were also seen.The aim of the research was to examine how effective all three diets were in a “real world” setting, where participants self-selected, which diet, they wished to follow, without any ongoing support from a dietitian.
Roy says the evidence shows that for some people the Mediterranean; fasting or paleo (Paleolithic) diets can be “healthful, beneficial ways to eat.”“This work supports the idea that there isn’t a single ‘right’ diet — there are a range of options that may suit different people and be effective. In this study, people were given dietary guidelines at the start and then continued with their diets in the real world while living normally. About half of the participants were still following their diets after a year and had experienced improvements in markers of health.
“Like the Mediterranean diet, intermittent fasting and paleo diets can also be valid healthy eating approaches — the best diet is the one that includes healthy foods and suits the individual.”The Mediterranean diet encouraged consumption of fruit, vegetables, whole-grain breads and cereals, legumes, nuts, seeds and olive oil with moderate amounts of fish, chicken, eggs and diary and red meat once a week or less.
The paleo diet consists of mostly less-processed foods with an emphasis on eating fruit and vegetables, animal proteins, nuts, coconut products and extra-virgin olive oil. While “original” Paleo diets strictly exclude all legumes, dairy and grains, this study used a modified version including some dairy as well as up to one serving daily of legumes and grain-based food.
Co-lead author Dr. Michelle Jospe, a Postdoctoral Fellow in the Department of Medicine, says the results showed people found the Mediterranean diet to be the easiest to adhere to.“Our participants could follow the diet’s guidelines more closely than the fasting and paleo diets and were more likely to stay with it after the year, as our retention rates showed.”
Most of the 250 participants (54 per cent) chose the fasting diet, while 27 per cent chose the Mediterranean and 18 per cent the paleo. After 12 months, the Mediterranean diet had the best retention rate with 57 per cent of participants continuing, with 54 per cent still fasting and 35 per cent still on the paleo diet.After 12 months, the average weight loss was 4.0kg for those choosing the fasting diet, 2.8kg on the Mediterranean diet and 1.8kg on the paleo diet.
Reduced systolic blood pressure was observed among those participating in the fasting and Mediterranean diets, together with reduced blood sugar levels in the Mediterranean diet. Jospe explains participants who said they were still following their diet at 12 months lost even more weight, showing the importance of choosing a diet that is sustainable. She believes the results of this study are relevant to the thousands of people following self-chosen diets with little supervision and indicates more realistic outcomes.