‘Cut out the sausage’ sums up much of the headline advice following recent research into meat consumption and fertility. Research by scientists from Harvard Medical School and Massachusetts General Hospital in the US, and Huazhong University of Science and Technology in China, studied the sperm of 141 men who were attending a fertility clinic. It was found that fertilisation rates in the laboratory were lower for men who consumed a diet high in processed meat. Sperm from men who ate more chicken, had a higher success rate.
The research, funded by the US National Institutes for Health and the China Scholarship Council, stopped short of making any firm recommendations, concluding instead that further research was required. While the study took into account confounding factors known to affect fertility, such as BMI or consumption of caffeine, it did not look at other lifestyle factors that may impact fertility.
The carbs vs fat debate has reignited following a recent study by scientists at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in the US. Since the publication of low-fat diets such as The Hip and Thigh diet in the late ‘80s, followed by the low-carb Atkins and Dukan diets, the jury has been constantly out on whether eating fewer carbohydrates or less fat is better for weight loss.
However in this latest study, it was found that subjects given a low-fat diet experienced a body fat loss at a staggering rate of 68 per cent higher than those given a low-carb diet. The small study, conducted on 19 non-diabetic, obese men and women gave subjects either low-fat or low carb calorie-equivalent diets. But although the low-fat diet produced higher weight-loss results, it did not have the same impact on insulin production or fat burning. The low-carb diet not only produced weight loss, but also lowered production of the fat-regulating hormone insulin and increased fat burning as expected, whereas fat restriction had no observed changes in insulin production or fat burning.
“Compared to the reduced-fat diet, the reduced-carb diet was particularly effective at lowering insulin secretion and increasing fat burning, resulting in significant body fat loss,” said Kevin Hall, PhD, NIDDK senior investigator and leadstudy author. “But interestingly, study participants lost even more body fat during the fat-restricted diet, as it resulted in a greater imbalance between the fat eaten and fat burned. These findings counter the theory that body fat loss necessarily requires decreasing insulin, thereby increasing the release of stored fat from fat tissue and increasing the amount of fat burned by the body.”
Participants stayed at a clinical unit for 24 hours per day for two extended visits, eating the same food and doing the same activities. For the first five days of each visit they ate a baseline balanced diet. Then for six days, they were fed diets containing 30 per cent fewer calories, achieved by cutting either only total carbs or total fat from the baseline diet, while eating the same amount of protein. They switched diets during the second visit.
But before you ditch the healthy fats from your fridge, it is thought that the gap between the two diets would eventually close over time. NIDDK said that researchers had previously simulated the study with a mathematical model of human metabolism, whose body fat predictions matched the data later collected in the study. When simulating what might happen over longer periods, the model predicted relatively small differences in body fat loss with widely varying ratios of carbs to fat. Those results suggested the body may eventually minimise differences in body fat loss when diets have the same number of calories. Also, further research would be needed to assess the physiological effects and health implications of fat and carb reduction in the long term.
A recent Canadian study has concluded that saturated fats do not pose the risk to health found with trans fats. The research, carried out at McMaster University, the University of Toronto, St Michael’s Hospital Toronto, Hamilton Health Sciences, and the Hospital for Sick Children Toronto, and published in the BMJ, looked at 70 previous studies but found no evidence that eating higher amounts of saturated fat, compared to low amounts, raised the risk of death, heart disease, stroke or diabetes. This contrasted against conclusions that eating more trans fats was linkedto an increased risk of death or heart disease.
While some headlines following the research have suggested eating more saturated fats could be healthy the study, which was funded by the World Health Organization, does not conclude this. The authors stated that further research was needed to examine the implications of fat consumption, because the results were based on observational studies that did not establish cause and effect.
According to the NHS, however, trans fats, which were typically found in processed foods, have been almost eliminated from the UK food chain, following previous fears of the impact on human health. The NHS website states: “In fact, due to the negative publicity surrounding trans fats in recent years, food manufactures have virtually removed trans fats from the UK food chain. Most brands of margarine now contain no, or only trace elements, of trans fats.” 
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