- Dietary polyphenols are beneficial plant chemicals found in fruit, herbs and vegetables, which are known primarily from their antioxidant action
- Most importantly, however, different polyphenols also exert anti-inflammatory, anti-cancer, metabolic and anti-obesity action on the human body
- In fact, scientists now know that it is not the antioxidant action that is important in polyphenols but the action on inflammation and metabolism
- EGCG (from green tea), resveratrol (found in berries), quercetin (found in onions), curcumin (from turmeric), catechins (in cocoa), epicatechins (in pine bark and grape seeds), proanthocyanidins (e.g. in cranberries), and myricetin (found in fruit) are some of the most "famous" polyphenols
- A review published in 2014 reports that thousands of cell, tissue, animal and human studies in the last few years have shown the beneficial effects of polyphenols on health, and specifically in metabolic disorders and obesity
- Cell studies show that dietary polyphenols fight fat in multiple ways. They:
- Reduce the life span of adipocytes (fat cells)
- Reduce fat cell growth
- Inhibit the capacity of fat cells to accumulate fat
- Reduce fat cell proliferation
- Stimulate lipolysis (fat breakdown and release from fat cells)
- Boost energy expenditure / fat oxidation ("fat burning") outside fat cells
- Stimulate thermogenesis (fat burning inside fat cells)
- Inhibit adipose tissue inflammation within and outside adipose tissue
- Fight oxidative damage within and outside fat tissue
- Fight metabolic dysfunction within and outside adipose tissue
- Reduce high glucose levels, triglycerides, cholesterol and glycation
- "Animal studies strongly suggest that commonly consumed polyphenols have a pronounced effect on obesity as shown by lower body weight, fat mass and triglycerides through enhancing energy expenditure and fat utilization, and modulating glucose homeostasis"
- "On the other hand, human studies are more limited and are more inconsistent about the anti-obesity impact of dietary polyphenols probably due to the various study designs and lengths, variation among subjects (age, gender, ethnicity), chemical forms of the dietary polyphenols used and confounding factors such as other weight-reducing agents", the study authors state
- However, our experience of reviewing such studies in the last decade shows that polyphenols are more effective on cell cultures, tissues and animals are more effective simply because of the much higher dosage than used on humans, which is quite often one or two orders of magnitude greater
- Nevertheless, the general trend with the use of polyphenols in human trials is towards a healthier metabolic profile and reduced fat accumulation, obesity and it's complications, even with normal, dietary intakes or with reasonably increased intakes in the form of supplements etc.
- However, polyphenols could be much more beneficial at local level, i.e. for spot fat / cellulite reduction than it is for whole body level. This is because whole body weight loss depends too much on food intake and exercise and because very high intake of polyphenols at whole body level is practically impossible and possibly unhealthy
- Clearly, high-concentration topical application, similar to that seen in cell, tissue and animal studies makes much more sense, and is a trend seen in quality cosmeceuticals recently, including anti-ageing and cellulite creams
- In all cases, more "randomised controlled trials are warranted to reconcile the discrepancies between preclinical efficacies and inconclusive clinic outcomes of these polyphenols", as the study authors report.
- Source: Novel insights of dietary polyphenols and obesity.
- Abstract: The prevalence of obesity has steadily increased over the past three decades both in the United States and worldwide. Recent studies have shown the role of dietary polyphenols in the prevention of obesity and obesity-related chronic diseases. Here, we evaluated the impact of commonly consumed polyphenols, including green tea catechins, especially epigallocatechin gallates, resveratrol and curcumin, on obesity and obesity-related inflammation. Cellular studies demonstrated that these dietary polyphenols reduce viability of adipocytes and proliferation of preadipocytes, suppress adipocyte differentiation and triglyceride accumulation, stimulate lipolysis and fatty acid β-oxidation, and reduce inflammation. Concomitantly, the polyphenols modulate signaling pathways including the adenosine-monophosphate-activated protein kinase, peroxisome proliferator activated receptor γ, CCAAT/enhancer binding protein α, peroxisome proliferator activator receptor gamma activator 1-alpha, sirtuin 1, sterol regulatory element binding protein-1c, uncoupling proteins 1 and 2, and nuclear factor-κB that regulate adipogenesis, antioxidant and anti-inflammatory responses. Animal studies strongly suggest that commonly consumed polyphenols described in this review have a pronounced effect on obesity as shown by lower body weight, fat mass and triglycerides through enhancing energy expenditure and fat utilization, and modulating glucose hemostasis. Limited human studies have been conducted in this area and are inconsistent about the antiobesity impact of dietary polyphenols probably due to the various study designs and lengths, variation among subjects (age, gender, ethnicity), chemical forms of the dietary polyphenols used and confounding factors such as other weight-reducing agents. Future randomized controlled trials are warranted to reconcile the discrepancies between preclinical efficacies and inconclusive clinic outcomes of these polyphenols.
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