Pomegranate juice, but not an extract, confers a lower glycemic response to a high–glycemic index food

This study was published in the American Journal of Clinical Nutrition

Words to know

Glycemic index (GI) – a reference value assigned to foods that relates to how slowly or quickly they can raise blood sugar levels after being eaten (pure sugar, or glucose = 100 and is used as a reference value)

Postprandial – occurring after a meal

Polyphenols – micro nutrients found in the diet that play a role in bodily processes and have many health promoting properties

 

Why is this study relevant?

With the increasing prevalence of metabolic diseases and diabetes in the U.S and throughout the world – strategies aimed at reducing risk factors associated with these diseases are warranted. The glycemic index (GI) of foods is continually relevant in the fact that reducing post-prandial (after a meal) blood sugar is key in maintenance and prevention of diabetes. Large swing in blood sugar are implicated in a variety of acute and chronic health conditions. High oscillations in blood sugar after a meal are the target of many current diabetic medications.

Pomegranate juice is rich in polyphenols, which are hypothesized by the authors to possibly play a role in the absorption of sugar by the intestine after a meal – and the sparse literature on pomegranate juice/polyphenols gives little evidence of an effect in either direction.

What’s the hypothesis?

Based on the available data and theorizing about interactions of various compounds, the authors hypothesize that pomegranate juice will benefit the post-prandial response of a meal. The mechanisms of this beneficial response are hypothesized to be due to the inhibition of carbohydrate digestion enzymes, which they will test in a non-human (in vitro) model.

Pomegranate Juice

The study measured the effects of both pure pomegranate juice as well as a pomegranate extract prepared from pomegranates and taken by the participants in pill form.

Who participated

  • Healthy individuals (47 total in 3 separate conditions)
  • No presence of disease
  • No special diets, supplements, medications
  • Normal fasting blood glucose

 

Study layout

Design

What did they find?

  •  Pomegranate extract inhibited enzymes related to carbohydrate breakdown and absorption (amylase, maltase-sucrase activity)
  • Pomegranate juice consumption decreased the glucose area under the curve (total response) by 33.1%
  • Pomegranate juice consumption also reduced peak glucose concentrations by 25.4%
  • No effect on blood glucose area under the curve/peak glucose after pomegranate polyphenol supplement consumption at low, medium, or high dose

 

Conclusions

 

Drink your pomegranate juice!

  • Polyphenol-rich pomegranate juice can reduce blood sugar spikes after a carbohydrate meal (bread)
  • The reduction in blood glucose AUC of 1/3 is quite substantial and had high significance
  • The polyphenol punicalagin may play a key role in the results, since it inhibits a carbohydrate digesting enzyme (amylase)

Lack of effectiveness when taken in supplement form?

  • Polyphenol supplement may be ineffective due to insufficient mixing in the stomach/intestine, although they demonstrated that the capsule material dissolved rapidly in stomach-like conditions

Juice vs. a drug?

  • Diabetic drug ‘acarbose’ administered to limit post-prandial blood glucose excursions, shows similar effectiveness (1/3 reduction)
  • Comparable to current study using pomegranate juice

 

Mechanisms!

Inkedamylase mechanism_LI
The blue circles represent areas where pomegranate juice is thought to intervene. 1. Conversion of starch to maltose by inhibiting amylase 2. inhibiting intestinal glucose uptake through transporter GLUT2 3. Glucose uptake into the liver and metabolism

Takeaways

Pomegranate juice has always been touted for its antioxidant benefits, touted as a “superfood” by many (thanks Dr. Oz). While I don’t buy into the “superfood” as a category, pomegranates sure do provide a variety of health benefits, many of which are just being discovered (as shown here). I believe that whole foods are always better than their constituent parts (in this case, juice vs. extracted polyphenols) and this I believe makes ecological and intuitive sense. Whatever benefits pomegranates have evolved to provide may only be maximally beneficial when in the presence of everything else the fruit has to offer. There are interactions among compounds that we can’t even fathom, and, when they’re all present in the amounts that nature grew them in, they work their magic. This logic holds true in the realm of vitamins – where we see that supplementing with an extract or pure compound rarely has the desired effects equal to that of eating an actual food.

Pomegranate juice might be an easy lifestyle implementation for diabetics (or anyone, I suppose) in terms of reducing blood sugar after a meal. In this study, they drank the juice pre-meal, allowed for the juice to “digest” and then fed the participants. Adding a glass seems like a simple strategy which may help benefit blood sugar control along with a boost of antioxidants and some vitamins.

Citation: Am J Clin Nutr. 2017 Oct 11. pii: ajcn161968. doi: 10.3945/ajcn.117.161968.

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