Past Week in Nutrition Science (April 29th–May 6th)

This is an overview of interesting nutrition research published from Friday, April 29th, to Friday, May 6th, 2016.

Female Doctor Holding Greens

Research Reviews

This week, we reviewed two papers: one on the importance of fiber to the gut microbiota and another about genetic adaptations to a vegetarian diet.

Review: Low-Fiber Diets Harm the Good Bacteria in Your Gut.

Article: The Fiber Gap and the Disappearing Gut Microbiome: Implications for Human Nutrition.

Summary: This review briefly discussed how low-fiber diets can reduce the counts of beneficial bacteria in the digestive system. Eating prebiotic fiber regularly may help preserve the good bacteria in your gut.

Review: Some People May Be Genetically Adapted to Vegetarian Diets.

Article: Positive Selection on a Regulatory Insertion–Deletion Polymorphism in FADS2 Influences Apparent Endogenous Synthesis of Arachidonic Acid.

Summary: This genetic study showed that a certain gene variant makes it easier for people to produce arachidonic acid from linoleic acid. The variant is found in 18% of North Americans and 68% of Indians. However, the health implications are unclear.

New Research From Around the World

Lots of new papers came to our attention this week. Here are summaries of the most interesting or relevant studies, categorized by subject.

1. Obesity and Weight Loss

Systematic review and meta-analysis of interventions targeting sleep and their impact on child body mass index, diet, and physical activity.

This systematic review suggests that sufficient sleep may improve the body mass index of children.

Is consuming yoghurt associated with weight management outcomes? Results from a systematic review.

This systematic review concluded that eating yogurt is associated with less weight gain, body fat, waist circumference and body mass index. However, a cause-and-effect relationship couldn’t be determined.

Lower core body temperature and greater body fat are components of a human thrifty phenotype.

Some people have a greater tendency to gain weight than others. This is not necessarily because they eat more — their bodies are simply better at preserving calories. These people are of the thrifty phenotype.

Thrifty individuals have a greater decrease in calorie expenditure during fasting. This study showed that thrifty individuals were more likely to have greater fat mass and belly fat. They also had a lower core body temperature.

Does artificial light-at-night exposure contribute to the worldwide obesity pandemic?

Previous studies indicate that light exposure at night may disrupt the body clock, affecting the daily fluctuations of neurotransmitters and promoting weight gain.

This observational study supports earlier evidence, suggesting that exposure to artificial light at nighttime may contribute to obesity.

2. Heart Health

Effect of vitamin D3 supplementation on blood pressure in adults: an updated meta-analysis.

This meta-analysis concluded that supplementing with vitamin D3 had no effects on blood pressure. However, when the daily dose was greater than 800 IU, blood pressure decreased in those who were 50 years or older.

The researchers also found that vitamin D3 may increase blood pressure when combined with calcium supplements.

Nitrate-Rich Vegetables Increase Plasma Nitrate and Nitrite Concentrations and Lower Blood Pressure in Healthy Adults.

This crossover trial showed that eating nitrate-rich vegetables — beetroot juice, rocket salad drink and a spinach beverage — increased circulating levels of nitrate and lowered blood pressure.

3. Appetite and Eating

Proximity of snacks to beverages increases food consumption in the workplace: A field study.

This field study, conducted at the Google offices, showed that snack consumption was higher when the snacks were placed closer to beverages.

Specifically, when snacks were placed close to beverages the likelihood of snacking increased from 12% to 23% for men and from 13% to 17% for women.

High perceived stress is associated with unfavorable eating behavior in overweight and obese Finns of working age.

This observational study found that self-perceived stress was linked with a higher risk of dysfunctional eating behaviors, such as uncontrolled eating, emotional eating and less intuitive eating.

4. Brain and Mental Health

Evaluation of the effects of iodized salt on the mental development of preschool-aged children: a cluster randomized trial in northern Ethiopia.

This randomized controlled trial examined the mental effects of giving iodized salt to iodine-deficient Ethiopian children who were 4–6 years old.

The study suggests that iodized salt does not affect brain function or mental performance in these children.

5. Lung Health

Dietary Cholesterol Increases the Risk whereas PUFAs Reduce the Risk of Active Tuberculosis in Singapore Chinese.

Tuberculosis is an infectious disease caused by a certain type of bacteria. It typically affects the lungs and is characterized by a persistent cough, bloody mucus and fever.

This observational study in Chinese men and women suggests that high amounts of dietary cholesterol may increase the risk of active tuberculosis. Marine omega-3 and omega-6 were linked to a reduced risk.

6. Digestive Health

Fermentable Carbohydrate Restriction (Low FODMAP Diet) in Clinical Practice Improves Functional Gastrointestinal Symptoms in Patients with Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a category of inflammatory conditions that affect the digestive tract. These include Crohn’s disease and ulcerative colitis.

This study suggests that a diet low in fermentable carbs, known as FODMAPs, may improve symptoms in people with IBD.

7. Liver Health

Are non-absorbable disaccharides associated with beneficial or harmful effects in people with cirrhosis and hepatic encephalopathy?

Cirrhosis is a chronic liver disease. Some people with cirrhosis may get hepatic encephalopathy (HE), which results in poor brain function. The accumulation of ammonia in blood is believed to play a key role in the development of HE.

Lactulose and lactitol are non-absorbable disaccharides (NAD) that reduce ammonia levels. This Cochrane review of randomized controlled trials concluded that supplementing with NAD may reduce the risk of HE, liver failure and death.

Strong and persistent effect on liver fat with a Paleolithic diet during a two-year intervention.

The Paleolithic diet is based on foods presumed to have been available in the Paleolithic period. These include whole foods such as fruits, berries, seeds, roots, meat and fish.

This randomized controlled trial showed that following the Paleolithic diet for one year decreased liver fat more than a conventional low-fat diet.

8. Muscles and Physical Performance

Effect of diet-induced weight loss on muscle strength in adults with overweight or obesity – a systematic review and meta-analysis of clinical trials.

This systematic review and meta-analysis suggests that losing weight by restricting calories may reduce muscle strength. To prevent this, dieting should be accompanied with strength exercises.

9. Men’s Health

Intake of Fruits and Vegetables with Low-to-Moderate Pesticide Residues Is Positively Associated with Semen-Quality Parameters among Young Healthy Men.

This observational study showed that eating fruits and vegetables high in pesticides was associated with decreased sperm counts in young men. This suggests that pesticides in food may reduce fertility.

10. Vitamins, Minerals and Other Nutrients

In Rwandese Women with Low Iron Status, Iron Absorption from Low-Phytic Acid Beans and Biofortified Beans Is Comparable, but Low-Phytic Acid Beans Cause Adverse Gastrointestinal Symptoms.

Phytate, found in beans, reduces the absorption of iron if eaten during the same meal. This study in Rwandese women showed that eating beans containing low amounts of phytate increased iron availability and reduced iron deficiency.

However, the researchers also found that low-phytate beans caused more digestive side effects, likely caused by higher amounts of phytohaemagglutinin L, a toxic lectin.