Past Week in Nutrition Science: This is an overview of interesting studies published on nutrition from Friday, Oct 30th, to Friday, Nov 6th, 2015.
Past Week in Nutrition Science (Oct 30th–Nov 6th)
This week we reviewed two research papers, one published in Pediatric Obesity and one from PLoS One.
Summary: This trial in obese children examined the short-term effects of reducing added sugar and replacing it with starch.
The study showed that this had multiple health benefits, including reduced blood pressure, lower blood cholesterol, decreased triglyceride levels and improved blood sugar control.
Summary: This was a meta-analysis of randomized controlled trials that compared the effectiveness of low-carb diets and low-fat diets on several factors. These were: body weight, risk factors for heart disease, blood lipids and blood pressure.
Low-carb diets turned out to be more effective for weight loss than low-fat diets, and better at reducing risk factors for heart disease.
New Research From Around the World
Tons of research papers were published this week, on a wide range of subjects.
New issues of the Journal of Nutrition, the American Journal of Clinical Nutrition and the British Journal of Nutrition came out, to name a few.
Below is a selection of the most interesting papers, organized by subject.
Obesity and Weight Loss
Diets that are high in resistant starch and/or protein have been found to be effective in weight management.
This randomized crossover study showed that a diet high in both resistant starch and protein increased the feeling of fullness and the amount of calories burned.
This study in young women shows that fluctuations in weight over a period of a few months may be a sign of future weight gain.
Poor sleep quality and short sleep duration are associated with obesity and metabolic syndrome. This observational study examined how this association changes with age.
Previous studies have suggested that high outdoor and indoor temperatures might increase the risk of obesity. This South Korean observational study supports this, with the authors mentioning adaptive thermogenesis as a possible explanation.
This 17-week randomized, weight-loss trial examined the effects of four standardized diets that varied in percentage of calories from carbs. The carb amount ranged from 55% to 70%.
The study showed that the percentage of calories from carbs did not affect changes in fat mass, lean mass and metabolic rate during weight loss. However, this study did not test the effectiveness of a low-carb diet.
This Australian observational study found that skipping breakfast was associated with higher body mass index (BMI) in both children and their mothers.
This cross-sectional observational study from Northern Germany found that potatoes and cakes were associated with increased belly fat.
Poor sleep quality and short sleep duration are associated with an increased risk for obesity. This randomized trial in healthy adults found that short sleep duration resulted in lower metabolic rate the morning after.
In other words, poor sleep causes the body to burn fewer calories. This association was stronger in African-Americans, compared to Caucasians.
Ghrelin is the appetite hormone. For this reason, high appetite is accompanied by high levels of ghrelin. Ghrelin levels fluctuate throughout the day, generally rising before meals and falling after meals.
This study found that ghrelin levels rose after a meal had started. This probably temporarily increased appetite during the meal. After the meal finished, ghrelin levels fell, as was expected.
This observational study suggests that diet quality is associated with a reduced risk of type 2 diabetes. However, it did not find any significant links between dietary diversity and central obesity or diabetes.
To improve metabolic health it is simply not enough to eat many different foods in moderation — these foods also have to be healthy.
This observational study suggests that healthy obesity is not associated with a healthy diet. In other words, overeating healthy food does not guarantee that you’ll become healthily obese. There are other, as yet, unknown factors at work.
This review discusses the possibility that the benefits of dietary calcium on obesity and diabetes could be affected by intestinal bacteria.
Blood Sugar Control and Type 2 Diabetes
Gliosis is a term that refers to changes in glial cells as a response to central nervous system damage. Glial cells are the most common cells in the nervous system. They surround neurons, supporting and insulating them.
This human study found an association between gliosis in the brain and insulin resistance. The association was independent of the amount of fat mass.
Bacteria in the digestive system, also called the gut microbiota, are affected by specific dietary patterns, especially if they are followed for a long period.
This randomized trial in obese individuals showed that following the Mediterranean diet, or a low-fat diet high in complex carbs, helped protect against type 2 diabetes by causing beneficial changes in the gut microbiota.
This randomized controlled trial in women with gestational diabetes suggests that soy protein may improve blood sugar control, lower triglycerides and reduce oxidative stress, compared to animal protein.
This large meta-analysis of observational studies did not find any significant links between red and processed meat intake and fasting glucose and insulin, after adjustment for other potential causal factors.
This meta-analysis of randomized controlled trials showed that the Mediterranean diet may improve blood sugar control, body weight and heart disease risk factors in people with type 2 diabetes.
This observational study suggests that long-term coffee consumption may protect against type 2 diabetes.
Although this doesn’t proove a causal relationship, anti-inflammatory compounds in coffee may possibly explain the association.
In general, this observational study did not find any significant associations between egg consumption and heart disease in individuals with diabetes.
However, it found an increased risk of heart failure in men when eggs were eaten more than once per day.
L-carnitine is a substance found in foods, such as red meat, and is also taken as a supplement. Dietary L-carnitine is changed into trimethylamine by bacteria in the digestive system. In the liver, it is metabolized into trimethylamine oxide (TMAO).
This mouse study indicates that TMAO may slow down the development of heart disease. More specifically, it can slow down the formation of lesions in the body’s main artery, the aorta.
Previous studies indicate that bacteria in the mouth may affect the development of diseases such as atherosclerosis.
This study showed that the bacterial community in the mouth was similar in healthy individuals and patients with atherosclerosis. However, patients with atherosclerosis had greater numbers of Anaeroglobus.
DASH stands for “dietary approaches to stop hypertension.” It is a dietary pattern designed and promoted by the US National Heart, Lung and Blood Institute.
This observational study suggests that following the DASH diet does not improve blood pressure in middle-aged adults.
Previous studies indicate that red and processed meats may have adverse effects on heart health. Conversely, seafood is believed to be protective, whereas the relevance of poultry is controversial.
This observational study found that long-term consumption of meat and poultry was associated with high blood pressure. Additionally, it found a weak but significant association between seafood and high blood pressure.
This meta-analysis combined the results of 6 trials examining the effects of the Mediterranean diet on high blood pressure.
The study found that following the Mediterranean diet for at least one year reduced blood pressure. However, the authors concluded that the evidence was weak.
This cross-sectional observational study in hemodialysis patients showed an association between processed meat intake and high blood pressure.
Some previous studies suggest that calcium supplements may increase the risk of heart disease.
This randomized controlled trial in post-menopausal women found that calcium supplements increased blood pressure and blood coagulation.
This observational study suggests that consuming dairy products may improve blood pressure.
This meta-analysis combined the results of 11 randomized controlled trials examining the effects of vegetarian diets on blood lipids.
The study showed that vegetarian diets effectively lower blood fats, including total cholesterol, LDL-cholesterol and HDL-cholesterol. For this reason, they may be useful for people with disorders that cause high levels of blood fats.
This cross-sectional observational study suggests that high fruit consumption may reduce blood triglyceride levels in South Korean people.
This 5-year randomized controlled trial in elderly people did not find any significant effects of selenium supplementation on circulating cholesterol levels.
Beta-sitosterol is a type of sterol found in plants, categorized as a phytosterol. This review discusses beta-sitosterol’s potential use in cancer treatment.
This study combined results from 15 observational studies. It found that high blood levels of retinol (vitamin A) were linked with an increased risk of prostate cancer.
Conversely, high levels of alpha-tocopherol (vitamin E) were associated with a reduced risk for prostate cancer.
High alcohol consumption has been associated with an increased frequency of sunburns, which is a risk factor for skin cancer.
This prospective observational study supports previous studies. Alcohol consumption was linked with a higher risk of skin cancer in both men and women.
Previous studies suggest that vitamin D may protect against cancer caused by tobacco use. This prospective observational study suggests that high vitamin D status may protect against tobacco-related cancers.
This meta-analysis of observational studies suggests that high intake of fruit and vegetables may protect against lung cancer. The association was stronger in women than men.
Brain and Mental Health
Previous studies suggest that long-chain omega-3 fatty acids, such as docosahexaenoic acid (DHA), are important for nervous system development.
This cross-sectional observational study indicates that good DHA status is linked with improved brain activity in developing children.
This observational study found that the children of obese mothers were, on average, less intelligent than children of normal-weight mothers. Additionally, mothers who gained more weight during pregnancy had children that were less intelligent.
DASH stands for “dietary approaches to stop hypertension.” It is a dietary pattern designed and promoted by the US National Heart, Lung and Blood Institute.
This observational study in Iranian adults found that following the DASH diet was associated with increased risk of depression.
FODMAPs are a category of carbs that are poorly absorbed. They may cause digestive discomfort in some people, especially those with irritable bowel syndrome or inflammatory bowel disease.
This randomized trial in patients receiving enteral nutrition showed that a diet low in FODMAPs improved diarrhea and nutritional status while also promoting recovery.
This observational study suggests that a diet high in vegetables and arctic marine mammals, such as seals, may improve lung function in Inuits from Greenland.
Higher Intakes of Fruits and Vegetables, β-Carotene, Vitamin C, α-Tocopherol, EPA, and DHA Are Positively Associated with Periodontal Healing after Nonsurgical Periodontal Therapy in Nonsmokers but Not in Smokers.
Periodontitis, or gum disease, is characterized by inflammation in the tissues that surround the teeth. It is caused by a strong immune reaction to the bacteria that live on the teeth.
This observational study found that high fruit and vegetable intake, including high amounts of beta-carotene, vitamin C and vitamin E, is associated with less periodontitis after treatment. This association was not significant in smokers.
This observational study in young, Australian adults found that diets high in protein, calcium and potassium were associated with higher bone mineral density.
This meta-analysis combined the results of 18 observational studies. It found that the risk of bone fractures was higher in children who avoided milk products and those who were not breastfed as infants.
Consuming a high amount of calories, cheese and sugar-sweetened beverages was also associated with an increased risk of fractures.
This observational study in elderly Norwegian adults found no association between circulating vitamin A or vitamin D and the risk of hip fractures.
Fertility and Pregnancy
Phytoestrogens are plant compounds that resemble the female sex hormone, estrogen. Nuts and soy products are among the richest dietary sources of phytoestrogens.
This observational study suggests that high levels of phytoestrogens in semen may indicate high male fertility and semen quality. However, they were not associated with couple fertility.
This observational study in children indicates that consuming high amounts of cow’s milk or milk formula in late infancy is associated with faster weight and height gain, compared to breastfeeding.
Immune Health, Inflammation and Infections
Tuberculosis is an infectious disease caused by a certain type of bacteria. It typically affects the lungs and is characterized by persistent cough, bloody mucus and fever. Individuals with tuberculosis are often vitamin D deficient.
This randomized controlled trial in tuberculosis patients found that vitamin D supplementation improved circulating vitamin D levels, but did not improve the symptoms of tuberculosis.
This mouse study indicates that excessive salt consumption may have harmful effects on the immune system. It may raise the risk of exaggerated inflammation and autoimmune disorders.
This small randomized crossover trial showed that eating garlic, 5 g/day for 10 days, increased the activity of 7 genes related to immune function, programmed cell death, and the metabolism of foreign substances in the body.
This meta-analysis concludes that vitamin D supplementation does not have any significant effects on systemic inflammation in obese and overweight people.
Allergies and Food Intolerances
According to this observational study, the amount of gluten eaten during late pregnancy is not associated with an increased risk of gluten intolerance in the child.
Macular degeneration is a condition that results in loss of vision because of damage to the retina of the eye. It usually affects elderly adults and is one of the main causes of blindness.
This observational study suggests that following the Mediterranean diet may protect against age-related macular degeneration. Genetic predisposition can modify this association.
Latent iron deficiency among pregnant mothers in India is associated with poor maturation of neurons involved with hearing in preterm infants.
This observational study indicates that higher intake of folate, beta-carotene and beta-cryptoxanthin may protect against hearing loss.
This observational study indicates that excessive calorie intake is associated with lower quality of life in elderly people.
This was a 2-year, randomized controlled trial that studied post-menopausal women. It found that supplementing with 30 grams of protein per day, on top of a diet that already provided adequate protein, did not increase muscle mass or physical function.
Vegetarian and Vegan Diets
This study showed that the diet of Danish vegans was low in certain micronutrients. It did not reach recommendations for protein, vitamin D, iodine and selenium. Among vegan women, vitamin A intake was also below recommendations.
On the other hand, the intake of added sugar, sodium and fat was more in accordance with official recommendations, compared to the general public in Denmark.
Vitamins and Minerals
This was a randomized crossover trial in healthy adults and patients with poor digestive absorption.
It showed that a mouth spray, containing vitamin D3, is more effective at raising circulating vitamin D levels than vitamin D in gelatin capsules.
Selenomethionine is the main form of selenium in the diet. After absorption, the liver converts it to selenide, the active form of selenium. However, this conversion is impaired in patients with liver disease, such as cirrhosis.
For this reason, patients with cirrhosis often have mild selenium deficiency. This randomized controlled trial showed that selenate is more effective than selenomethionine in patients with cirrhosis.
Taking vitamin E supplements with fat is presumed to increase vitamin E absorption. However, this randomized crossover study showed that absorption of vitamin E is not increased when it is taken with dairy fat, regardless of health status.
Additionally, the study found that people with metabolic syndrome have a lower alpha-tocopherol absorption, compared to healthy individuals.
This cross-sectional observational study found that higher body weight was associated with lower circulating vitamin D levels in adults with pre-diabetes.