Strawberry polyphenols mitigate very high dietary fructose-induced metabolic dysfunction in rats

This was an interesting paper that has been sitting in my drafts for awhile, so here is a quick post on it.

By Jaroslawska et al., it directly examines the ability of strawberry pomace (leftover from industrial processing of strawberries) to mitigate the adverse metabolic effects of a high fructose intake in rats in the blood and in the gut (unabsorbed fructose seems to alter gut physiology).

Dried strawberry pomace is made by removing the seeds of pressed strawberries (juice is removed) and air drying. The dry material is then granulated to pellets. The unappetizing result looks like this.  Polyphenols were identified and quantified by HPLC in 2 pomace preparations (‘native US abundant’ (US) & ‘extracted’ (EX)) and the dominant polyphenols were ellagitannins (84.5% & 73.6%, respectively). Both contained fiber with about 3% of it being soluble in each. The total polyphenols are much higher in the US preparation at 16.8 mg/g vs 5.5 mg/g in the extracted. They tested both preparations to make comparisons between a higher and lower dose of polyphenols.

48 male Wistar rats were split into 6 groups of 8 and fed the following for 4 weeks:

  1. corn starch (control)
  2. corn starch + US
  3. corn starch + EX
  4. fructose (control)
  5. fructose + US
  6. fructose + EX
The pomace made up about 7.7% of the diets. The fructose and corn starch made up about 60% of the diets (presumably to better detect differences). Here is the diet table:

 

The diets didn’t result in differing body weight of the rats (interesting) but the 3 groups consuming fructose had enlarged livers and kidneys compared to the starch groups. Supplementation with EX (with both corn starch and fructose) reduced kidney weights compared to their controls, but liver mass was unaffected.

 

The pH of cecal content was reduced in both of the US supplemented groups compared to their controls (both fructose and sucrose), and both types of supplementation (with both carbohydrate) had reduced ammonia concentrations in the cecal content as well compared to controls. The corn starch control had a higher ammonia content than the fructose control. Several and total short chain fatty acids in the cecal content were elevated with US supplementation along with both corn starch and fructose compared to controls. Together, the authors suggest these show that fermentable carbohydrates (soluble fiber) were what mitigated the dietary changes to renal function.

 

Fructose diets increased insulin concentrations compared to corn starch diets by nearly 2-fold, and insulin resistance was measurably higher. Rats fed US (but not EX) along with fructose had normalized insulin. Serum free fatty acids were also higher in fructose fed rats compared to corn starch, and again US only decreased this. Total serum cholesterol and triglycerides were increased in fructose fed rats, and while neither strawberry preparation affected cholesterol, US fed rats had reduced triglycerides. Atherogenic index (log (TG/HDL-C)) was higher in fructose fed rats which was reduced only in the US and corn starch fed rats (perhaps anomaly?). Fructose fed had increased ALT activity but not AST, which was reduced in the US supplemented groups. So the higher polyphenol content from the US pomace preparation prevented some of the liver dysfunction in response to high fructose intake causing insulin resistance.

 

Hepatic triglycerides and cholesterol was also increased in fructose fed rats compared to starch, and both US and EX reduced triglycerides and cholesterol in the fructose groups.

 

The group measured TBARS in the heart as a measure of antioxidant protection, which i’m not sure is sufficient for much confidence by itself, but it was higher in fructose fed rats, and lower in the US and EX supplemented groups.

 

Hepatic lipid peroxidation was increased in fructose fed rats and was not reduced with any of the strawberry treatments. Liver conjugated diene was lowered in US moreso than EX and fructose fed rats. In fructose fed rats, antioxidant capacity of hydrophilic substances in the serum (ACW) was increased with both strawberry supplements but moreso with US. ACL (antioxidant capacity of lipophilic substances in serum) was increased with both US and EX.

 

There are several mechanisms in which the polyphenols and fiber in the strawberry could be affecting these various measures that i’ll be discussing in future posts, but let me know if you’d like a copy of the paper in the comments.

 

Reference

Jaroslawska, J., Juskiewicz, J., Wroblewska, M., Jurgonski, A., Krol, B., & Zdunczyk, Z. (2011). Polyphenol-Rich Strawberry Pomace Reduces Serum and Liver Lipids and Alters Gastrointestinal Metabolite Formation in Fructose-Fed Rats Journal of Nutrition, 141 (10), 1777-1783 DOI: 10.3945/jn.111.143677

  • LRomeo

    Interesting article. I would like a copy of the paper.

    • http://www.nutsci.org Colby

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