Monday, August 18, 2014

Hormonal Responses to Food Intake Begin in Your Mouth

ChewOnThisLogoIn my current show at the 33rd Edmonton International Fringe Theatre Festival, I joke about the importance of chewing your food. This has classically been noted to be of importance to allow the enzymes in saliva to begin the process of digestion.

However, now a fascinating study by Yong Zhu and colleagues from Iowa State University, published in Physiology and Behaviour shows that chewing prompts hormonal changes that vary based on the composition of the food.

In their study, ten healthy males volunteers underwent a sham-feeding experiments (you chew but do not swallow your food) after an overnight fast with 3-min chewing of water, high-fat (nuts), high-carbohydrate (cereal) or high-protein (cheese) food provided in a randomized order (on four separate occasions).

While plasma glucose levels increased slightly and plasma lipids decreased slightly after all test foods, the high-carbohydrate food elicited significantly higher insulin, and the high-protein food resulted in higher ghrelin compared to other test sessions.

The authors attribute these changes in part to neuronal signals transmitted through the vagal nerve, which can for e.g. stimulate glucagon release, thereby explaining the observed increase in plasma glucose levels after all foods.

This study shows that short-term oral exposure to different foods can result in metabolic and hormonal changes that are partly dependent on diet composition.

If nothing else, this study points to the fact that chewing is not simply about mechanically preparing food for swallowing – it is far more a process that puts the organism into a nutritive state with distinct metabolic and hormonal changes.

Chew your food!

@DrSharma
Edmonton, AB

ResearchBlogging.orgZhu Y, Hsu WH, & Hollis JH (2014). Modified sham feeding of foods with different macronutrient compositions differentially influences cephalic change of insulin, ghrelin, and NMR-based metabolomic profiles. Physiology & behavior, 135, 135-42 PMID: 24952264

 

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Thursday, July 31, 2014

Low Adipocyte Formation Is Associated With Abdominal Obesity

sharma-obesity-adipocytes3One of the key concepts about the deposition of visceral and ectopic fat is the inability of “healthy” subcutaneous to readily expand to accommodate excess calories. This is why people with large fat cells and those with less or no subcutaneous fat (as in partial or complete lipodystrophy) display features of the metabolic syndrome.

In line with these observations, a study by Andre Tchernof and colleagues from the University of Laval, Quebec, in a paper published in ADIPOCYTE show that low adipogenic capacity of subcutaneous adipose tissue is associated with visceral obesity, visceral adipocyte hypertrophy, and a dysmetabolic state.

The researchers studied adipocytes and preadipocytes isolated from subcutaneous and visceral fat samples from 35 women undergoing gynecological surgery and assessed body fat distribution by CT as well as fasting plasma lipids and glycemia.

Using an in vitro differentiation assay, they found that lower adipogenic rates were strongly associated with increased visceral cell size and dyslipidemia.

In addition, When matched for BMI, women with low subcutaneous preadipocyte adipogenic rates had a higher visceral adipose tissue area, omental adipocyte hypertrophy, higher VLDL-lipid content and higher fasting glycemia.

All of these findings are in line with the notion that low subcutaneous preadipocyte differentiation capacity in vitro is associated with visceral obesity, visceral adipocyte hypertrophy, and a dysmetabolic state.

Once again, as regular readers should be aware, not all fat is equal.

@DrSharma
Edmonton, AB

ResearchBlogging.orgLessard J, Laforest S, Pelletier M, Leboeuf M, Blackburn L, & Tchernof A (2014). Low abdominal subcutaneous preadipocyte adipogenesis is associated with visceral obesity, visceral adipocyte hypertrophy, and a dysmetabolic state. Adipocyte, 3 (3), 197-205 PMID: 25068086

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Wednesday, July 30, 2014

Prebiotic Fibre Alters Mother Milk and Offspring Gut Bacteria in Rats

sharma-obesity-suckling-rat1With all the attention to the role of gut microbiota and the ongoing debate as to the role of breast feeding in obesity prevention, a study by Raylene Reimer and colleagues from the University of Calgary adds an interesting spin.

Their study, now published in OBESITY shows that feeding female rat a diet high in prebiotic fibre (21.6% wt/wt) throughout pregnancy and lactation, compared to a control or high-protien (40% wt/wt) diet, results in a lower oligosaccharide content of the milk with a higher content of bifidobacteria in the offspring.

Although this did not lead to any marked differences in body composition or other metabolic parameters, the study proves the point that (at least in rats) maternal diet can affect the composition of gut bacteria in the offspring (which may or may not have metabolic benefits).

There is no reason to believe that in humans maternal nutrition may well impart a similar influence via breast feeding on the microbiota of infants.

This certainly sounds like a promising field for future research.

@DrSharma
Edmonton, AB

ResearchBlogging.orgHallam MC, Barile D, Meyrand M, German JB, & Reimer RA (2014). Maternal high protein or prebiotic fiber diets affect maternal milk composition and gut microbiota in rat dams and their offspring. Obesity (Silver Spring, Md.) PMID: 25056822

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Tuesday, July 15, 2014

The Molecular Biology of Food And Mood

sharma-obesity-brainThe neuroendocrine systems that control ingestive behaviour are intimately linked to the parts of the brain that control mood.

Thus, it is increasingly evident that factors that affect energy homeostasis (diet and exercise) can have profound effects on mood while changes in mood can have significant effects on appetite and energy homeostasis.

But this relationship is far from straightforward – rather, it appears to be rather complex.

Readers interested in an overview of how these two systems interact in the brain may find a recent review by Chen Liu from the University of Texas Southwestern Medical Center, Dallas, published in Cell Metabolism of interest.

The authors review our current understanding of how mood and food are linked with particular attention to appetite, ingestive behaviour and energy homeostasis.

The article also touches on the effects of pharmacological and surgical treatments for obesity on mood.

Clearly clinicians need to be aware of the close links between these systems and draw on our current understanding of both in their counselling of patients presenting with weight gain and/or depression.

@DrSharma
Edmonton, AB

ResearchBlogging.orgLiu C, Lee S, & Elmquist JK (2014). Circuits Controlling Energy Balance and Mood: Inherently Intertwined or Just Complicated Intersections? Cell metabolism, 19 (6), 902-909 PMID: 24630814

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Thursday, July 10, 2014

Can Germs In Your Drinking Water Help Prevent Obesity?

sharma-obesity-tap-water1In my show I joke about how I intend to import water from the river Ganges as a new obesity treatment that I will appropriately name “RunFast”.

Jokes aside, a study by Zhongyi Chen and colleagues, published in the Journal of Clinical Investigation, shows that treating mice with genetically modified bugs delivered through their drinking water can protect them from becoming obese even when fed a high-fat diet.

To be exact, the researchers used a strain of e coli bacteria genetically engineered to produce N-acylphosphatidylethanolamines (NAPEs), which are precursors to the N-acylethanolamide (NAE) family of lipids, normally synthesized in the small intestine in response to feeding and known to reduce food intake.

As their study shows, administration of these modified bacteria in drinking water for 8 weeks dramatically lowered food intake, weight gain, body fat, insulin resistance and liver fat in mice on a high-fat diet.

These “protective effects” lasted for at least 4 weeks after removal of these bacteria from the drinking water.

In another set of experiments the researchers also showed that this strain of bacteria reduced weight gain in a genetic model of mouse obesity.

Contrary to what one may believe, this study neither supports nor refutes the idea that gut bacteria may be partly responsible for the obesity epidemic.

Rather, the study primarily shows that bacteria may be used as a delivery system for “therapeutic doses” of molecules to the intestines – in this case, resulting in the modification of appetite and metabolism.

I would not be surprised if the therapeutic use of bacteria (genetically modified or not) opens up a whole new dimension of therapeutics – not just for obesity.

@DrSharma
Edmonton, AB

ResearchBlogging.orgChen Z, Guo L, Zhang Y, L Walzem R, Pendergast JS, Printz RL, Morris LC, Matafonova E, Stien X, Kang L, Coulon D, McGuinness OP, Niswender KD, & Davies SS (2014). Incorporation of therapeutically modified bacteria into gut microbiota inhibits obesity. The Journal of clinical investigation PMID: 24960158

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In The News

Diabetics in most need of bariatric surgery, university study finds

Oct. 18, 2013 – Ottawa Citizen: "Encouraging more men to consider bariatric surgery is also important, since it's the best treatment and can stop diabetic patients from needing insulin, said Dr. Arya Sharma, chair in obesity research and management at the University of Alberta." Read article

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