Walnuts, Beans & Cacao - Anti-Cancer, Anti-Colitis, Anti-Diabetes (Super-)Foods that May Fail the Reality Check

Walnuts, cacao and beans, 3 superfoods that are super only in super-high quantities.

Today's SuppVersity Food Science Research Update is all about three so-called "superfoods". It's an article from which you cannot just learn that walnuts, beans and cacao are "superfoods" as they protect you from cancer, improve your gut health and ameliorate diabetes.

It's yet also an article that puts the (rodent) science into perspective. A perspective you won't see taken very often, because it has the "superfoods" look much less "super" than they appear to be without a reality check.

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• Dietary walnut suppression of colorectal cancer in mice: Mediation by miRNA patterns and fatty acid incorporation - As a SuppVersity reader you are well aware of the beneficial health effects of regular walnut consumption. As far as the mechanisms are concerned, many of you may have speculated that it is related to omega-3s, but do walnuts even have enough omega-3s to make a difference? A recent study from the Beth Israel Deaconess Medical Center at the Harvard Medical School (Tsoukas. 2015) seems to have found the answer is "yes", but it takes some serious walnut eating.
  
  To investigate the protective effects of a high walnut diet, the scientists injected rodents with HT-29 colon cancer cells. 7 days after the injection, the mice were randomized to either control or walnut diets for 25 days of diet treatment. After the study period, thirty samples of tumor and of omental adipose were analyzed to determine changes in lipid composition in each dietary group in response to diets containing either no or 10% (of weight) walnuts.
  

  

  Figure 1: Gas chromatography analysis of fatty acids in colorectal tumors (left) and omental adipose tissue (right) in 30 mouse samples (Tsoukas. 2015). *P<.05.

  In the tumors of the walnut-containing diet, the scientists found significant increases in α-linolenic, eicosapentaenoic, docosahexaenoic and total omega-3 acids, and a decrease in arachidonic acid, as compared to the control diet.
• More importantly, however, the final tumor size measured at sacrifice was negatively associated with percentage of total omega-3 fatty acid composition (r=−0.641, P=.001). MicroRNA expression analysis of colorectal tumor tissue revealed decreased expression of miRNAs 1903, 467c and 3068 (P<.05) and increased expression of miRNA 297a* (P=.0059) in the walnut-treated group as compared to control diet... and YES! This is the epigenetic "magic" everyone is talking about.
• Beans are SFCA-precursors and colon protectors - Short-chain fatty acids are all the rage these days. SFCAs are the fatty acids that are produced by our bacterial subtenants when we eat resistant starches.
  
  Beans are an excellent source of resistant starches and, according to a recent study from the Agriculture and Agri-Food Canada (Monk. 2015), both cooked white (WK) or dark red kidney (DK) bean flour can, when it is added at 20% to a rodent diet  for 3 weeks, can protect rodents from the pro-colitic assault of dextran sodium sulfate.
  

  

  Figure 1: Effect of kidney bean diets on (A) SCFA concentrations, (B) cecum size and (C) colon histomorphology in healthy mice + representative images (40×) of  stained colon sections stained highlighting the increased crypt height in the bean-fed mice are shown (scale bar=50μm | Monk. 2015).

  Not only did the "bean preload" (a) reduce the disease severity. It did also ameliorate (b) the colonic histological damage and (c) increase the mRNA expression of antimicrobial and barrier integrity-promoting genes (Toll-like Receptor 4 (TLR4), MUC1–3, Relmβ and Trefoil Factor 3 (TFF3)) and reduce proinflammatory mediator expression [interleukin (IL)-1β, IL-6, interferon (IFN)γ, tumor necrosis factor (TNF)α and monocyte chemoattractant protein-1], which correlated with reduced colon tissue protein levels.
  
  In conjunction with their beneficial effects on IL-17A, IFNγ, TNFα, IL-1β and IL-6, there's little doubt that bean floor can enhance the microbial-derived SCFA metabolite production, gut barrier integrity and the microbial defensive response in the healthy colon, this making it more resilient to artificial and natural assaults.
• Cocoa-rich diet ameliorates hepatic insulin resistance by modulating insulin signaling and glucose homeostasis in Zucker diabetic fatty rats  - While the latest "eat chocolate to lose weigh" paper has been busted, findings of a recent study from the Ciudad Universitaria suggest that cocoa, not chocolate, has the potential to alleviate both hyperglycemia and hepatic insulin resistance in type 2 diabetics - in rats, it already works (Cordero-Herrera. 2015).
  
  In the study, male Zucker diabetic fatty (ZDF) rats which are a common model for "lifestyle" diabetes were fed a control or cocoa-rich diet (10%), and Zucker lean animals received the control diet. ZDF rats supplemented with cocoa (ZDF-Co) showed a significant decrease in body weight gain, glucose and insulin levels, as well as an improved glucose tolerance and insulin resistance.
  

  

  Figure 1: Effect of the cocoa-rich diet on glucose tolerance and insulin resistance in ZDF rats. (A) Time-course changes in the basal level and after glucose loading (1 g/kg) of blood glucose. (B) AUC calculated from GTT data. (C) Time-course changes in the basal level and after glucose loading (1 g/kg) of serum insulin. Each point represents the mean±S.D. from 8 determinations. (D) HOMA-IR was determined as described in Materials and Methods (p < 0.05 | Cordero-Herrera. 2015).

  The cocoa-rich diet also ameliorated the hepatic insulin resistance by abolishing the increased serine-phosphorylated levels of the insulin receptor substrate 1 and preventing the inactivation of the glycogen synthase kinase 3/glycogen synthase pathway in the liver of cocoa-fed ZDF rats - or put simply, it kept the glycogen storage (and thus another way to store glucose and normalize the blood glucose levels) in the liver intact.
  
  The authors believe that this anti-hyperglycemic effect of cocoa must at least partly be mediated through the decreased levels of hepatic phosphoenolpyruvate carboxykinase which will have the liver pump out more glucose (made mostly from amino acids) although the glucose levels in the blood are already in the red zone while increasing the values of the previously mentioned glucokinase and glucose transporter 2 in the liver which will allow cacao aficionados to store the superfluous glucose as glycogen, not fat. The additional suppression of the c-Jun N-terminal kinase and p38 activation which is usually elevated in response to insulin resistance may also protect you against cancer.

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So what have you learned today? You've learned that walnuts, beans and cacao are what other people may call "superfoods". Since this is the SuppVersity and not your next-best "natural * whatever * bogus * blog" I will now tell you that there's a huge caveat with these impressive data: DOSAGE! In the walnut study, for example, the food contained 100g/kg cacao powder that's 10% of the diet being pure cacao. The same goes for the walnut diet in the Tsoukas study. 10% walnuts in the diet, that's 65% of the total energy intake from walnuts and would equal 205g of walnuts for someone on the standard 2000kcal/day diet that's also used for the calculations on the nutrition labels.

If you think you can stomach that and - at the same time - cut the caloric equivalent of those 205g of walnuts from your "regular diet" in order not to get fat, go for it, but let's be honest: You don't really want to eat that "super", do you? No, you don't, but that's not a problem. Food is food and the aforementioned foods are still healthy, even if you don't eat them in the quantities that would be necessary to achieve "medicinal" effects | Comment on Facebook!

References:

• Cordero-Herrera, Isabel, et al. "Cocoa-rich diet ameliorates hepatic insulin resistance by modulating insulin signaling and glucose homeostasis in Zucker diabetic fatty rats." The Journal of nutritional biochemistry (2015).
• Monk, Jennifer M., et al. "White and dark kidney beans reduce colonic mucosal damage and inflammation in response to dextran sodium sulfate." The Journal of nutritional biochemistry (2015).
• Tsoukas, Michael A., et al. "Dietary walnut suppression of colorectal cancer in mice: Mediation by miRNA patterns and fatty acid incorporation." The Journal of nutritional biochemistry (2015).