Past Week in Nutrition Science (May 20th–27th)

This is an overview of interesting nutrition research published from Friday, May 20th to Friday, May 27th, 2016.

Here are some of the more interesting findings this week:

Slow metabolism is not to blame for obesity.
Fatty acids produced by gut bacteria affect appetite.
Early-life body composition may affect later weight.
Decreasing salt intake may reduce blood pressure.
Soy does not significantly affect inflammatory markers.
Certain foods may reduce the risk of depression.
Vitamin D may have benefits for fertility.

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Research Reviews

This week we reviewed two papers: one on the association of obesity with calorie expenditure and another on a randomized controlled trial examining the effects of short-chain fatty acids on reward-driven eating behavior.

Review: Is Weight Gain Caused by a “Slow Metabolism”?

Article: Is Obesity Associated with Altered Energy Expenditure?

Summary: This review looked at the available evidence linking obesity with changes in calorie expenditure.

The authors concluded that obese people burn more calories at rest, compared to non-obese individuals. Therefore, slow metabolism is not to blame for obesity, at least not in the majority of people.

Review: Fatty Acids Produced by Gut Bacteria Reduce Appetite.

Article: Increased colonic propionate reduces anticipatory reward responses in the human striatum to high-energy foods.

Summary: This randomized controlled trial examined the effects of elevated colonic propionate formation on calorie intake and food reward-driven eating behavior in humans.

The study showed that increased levels of propionate in the colon affected brain signals linked to appetite regulation, reduced calorie intake and decreased the appeal of high-calorie foods.

New Research from Around the World

A number 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

Appetite-regulating hormones in early life and relationships with type of feeding and body composition in healthy term infants.

Body composition early in life may affect people’s risk of becoming obese later in life. Levels of appetite hormones might play a role in this association.

This observational study in preterm infants found that breastfeeding was linked to higher levels of ghrelin, leptin and insulin, compared to formula-feeding. These results suggest that breastfeeding may protect against weight gain and obesity.

Higher Dietary Choline and Betaine Intakes Are Associated with Better Body Composition in the Adult Population of Newfoundland, Canada.

This observational study in Canadian adults found that choline and betaine intakes were associated with reduced body fat. These findings are supported by animal studies.

Choline is an essential nutrient found in high amounts in eggs, liver and fish roe (caviar), whereas betaine (trimethylglycine) is found in quinoa, spinach and beets, to name a few.

No insulating effect of obesity.

Scientists have speculated that high levels of body fat might insulate against cold, reducing the calorie expenditure associated with heat loss.

However, this study in mice suggests that obesity does not reduce heat loss. Human studies are needed before any strong conclusions can be reached.

Breakfast consumption and weight-loss maintenance: results from the MedWeight study.

This observational study suggests that men who regularly eat breakfast are more likely to be successful at maintaining their weight after a weight-loss program. A similar association was not seen in women.

Associations between eating frequency and energy intake, energy density, diet quality and body weight status in adults from the USA.

This observational study of US adults found that higher eating frequency was associated with a lower energy density of the foods eaten and a higher score on the Healthy Eating Index 2010.

High eating frequency was also linked to a lower body mass index in women and a lower waist circumference in both men and women.

2. Blood Sugar Control and Diabetes

Egg consumption and risk of incident type 2 diabetes: a dose–response meta-analysis of prospective cohort studies.

This meta-analysis of prospective observational studies found that high egg consumption was linked to a greater risk of developing type 2 diabetes.

When the studies were analyzed depending on country, the association turned out to be significant only in the US. The authors concluded that the results might be explained by other lifestyle factors associated with egg consumption.

3. Heart Health

Association Between Protein Intake and Mortality in Hypertensive Patients Without Chronic Kidney Disease in the OLD-HTA Cohort.

Some studies indicate that protein intake may help protect against high blood pressure and heart disease. However, this is still a matter of debate.

This observational study in people with high blood pressure found that protein intake above 0.32 g for each pound (or 0.7 g for each kg) of their ideal body weight reduced the risk of death from heart disease or all causes.

Healthful Dietary Patterns and the Risk of Hypertension Among Women With a History of Gestational Diabetes Mellitus: A Prospective Cohort Study.

Women with type 2 diabetes are at an increased risk of developing high blood pressure later in life.

This observational study showed that adhering to healthy dietary patterns, such as the alternative Healthy Eating Index 2010, the DASH diet or the alternative Mediterranean diet, was linked to a lower risk of developing high blood pressure.

Modest Salt Reduction Lowers Blood Pressure and Albumin Excretion in Impaired Glucose Tolerance and Type 2 Diabetes Mellitus: A Randomized Double-Blind Trial.

This 12-week randomized controlled trial examined the effects of modest dietary salt reduction on blood pressure in people with poor blood sugar control and normal or mildly-elevated blood pressure.

The study showed that a modest reduction in salt intake, or approximately 2.9 grams, led to a clinically relevant decrease in blood pressure.

4. Cancer

The Effect of Reduced Dietary Fat and Soy Supplementation on Circulating Adipocytokines in Postmenopausal Women: A Randomized Controlled 2-Month Trial.

Previous observational studies in Asian women have suggested that regularly eating soy products may reduce the risk of breast cancer by decreasing inflammation. However, short-term trials have found limited effects of soy on inflammatory markers.

This 8-week trial in postmenopausal women examined the effects of supplementing with either 50 mg/day of soy isoflavones, 15 g/day of soy protein from tofu or following a very low-fat diet. None significantly affected inflammatory markers.

Association of Vitamin D Levels With Outcome in Patients With Melanoma After Adjustment For C-Reactive Protein.

Melanoma is a type of skin cancer. The main risk factors are excessive exposure to ultraviolet light, sunburns and pale skin.

This observational study showed that higher circulating levels of vitamin D were associated with better treatment outcomes in patients with melanoma. High vitamin D levels were also linked to lower levels of the inflammatory marker CRP.

5. Brain and Mental Health

The effect of daily zinc and/or multivitamin supplements on early childhood development in Tanzania: results from a randomized controlled trial.

This randomized controlled trial in Tanzanian infants showed that supplementing with zinc and/or multivitamins (vitamins C, E and a B-complex) for one year had no effects on their mental development, compared to a placebo.

Curcumin and cognition: a randomised, placebo-controlled, double-blind study of community-dwelling older adults.

Previous studies examining the effects of curcumin on mental function have provided mixed results. This 12-month randomized controlled trial in older adults examined the effects of supplementing with 1500 mg/day of BiocurcumaxTM.

The study suggests that curcumin may prevent a decline in mental function, according to the Montreal Cognitive Assessment. However, other measurements revealed no significant effects.

The association between dietary patterns derived by reduced rank regression and depressive symptoms over time: the Invecchiare in Chianti (InCHIANTI) study.

This prospective observational study examined the association of food groups or dietary components with depressive symptoms.

It showed that a diet rich in vegetables, olive oil, grains, fruits and fish and moderate in wine and red meat were consistently linked to a lower risk of depression.

6. Liver Health

There are concerns that supplementing with a green tea extract may cause liver damage in some people. This systematic review of randomized controlled trials suggests that liver damage after eating green tea extract is rare.

Randomized controlled trials have reported no serious liver-related side effects, and most cases were mild. Currently, normal intake of green tea extract is considered safe in healthy people.

7. Muscles and Physical Performance

Carbohydrate mouth rinsing has no effect on power output during cycling in a glycogen-reduced state.

This small study compared the effects of carb mouth rinsing and carb consumption on power output among male cyclists who had fasted overnight.

The study showed that eating carbs after fasting increased power output during cycling, compared to a placebo. In contrast, mouth rinsing with carbs had no such effects.

The impact of post-exercise hydration with deep-ocean mineral water on rehydration and exercise performance.

Deep-ocean mineral water (DMW) is found at ocean depths of 820–4,921 ft (250–1,500 meters) and rich in various minerals. This study suggests drinking DMW may result in faster rehydration, compared with spring water or a carb-based sports drink.

8. Arthritis

Omega-3 fatty acids are associated with a lower prevalence of autoantibodies in shared epitope-positive subjects at risk for rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that affects the joints. The main symptoms are swollen and painful joints, most commonly in the hands. It may eventually lead to deformed joints and physical disability.

This observational study suggests that dietary intake of omega-3 fatty acids may reduce RA in a subgroup of people at risk, specifically those with HLA class II genetic susceptibility to RA.

9. Blood

An open-label randomized parallel-group comparative study of the efficacy of sorghum bicolor extract in preoperative anemia.

Sorghum is the world’s fifth most common cereal crop.

This study in anemic patients showed that supplementing with 5mg/day of folic acid, 200 mg/day of iron and 500 mg/day of sorghum extract didn’t significantly improve anemia, compared to folic acid and iron alone.

Effects of two therapeutic dietary regimens on primary chylomicronemia in paediatric age: a retrospective data analysis.

Primary chylomicronemia (PC) is a rare genetic disorder characterized by high blood levels of lipoproteins known as chylomicrons, resulting in excessive circulating levels of triglycerides. People with PC are at a high risk of inflammation in the pancreas.

This study in children with PC showed that following a low-fat diet and supplementing with omega-3 fats for at least 5 months caused a significant decrease in triglyceride levels. Further studies are needed to assess the long-term effects of this treatment.

10. Women’s Health

Vitamin D Status Relates to Reproductive Outcome in Women with Polycystic Ovary Syndrome: Secondary Analysis of a Multicenter Randomized Controlled Trial.

Polycystic ovary syndrome (PCOS) is characterized by cysts on the ovaries and an imbalance in hormone levels. This may lead to difficulties getting pregnant, irregular periods and an increased risk of diabetes and heart disease.

This observational study in women with PCOS found that high circulating levels of vitamin D were associated with increased fertility following a fertility treatment known as ovulation induction.