Last year was the year of the acai berry. Mangosteen, noni, goji, and others also proliferate on the juice and supplement market. Some are predicting what will be next. Are these so called “superfruits” any better than “regular” fruit?
Let’s look at a few lines of evidence.
What makes a fruit “super”?
First of all, we have to define what characteristics a fruit has to have to be labeled “super.” The superfruit craze seems to have hit a tipping point in 2004, however there appear to be no clear standards as to how a fruit attains a “super” status. Marketing and exotic appeal rather than science have given select fruits a more salubrious appeal. As most health claims however, these are based on perception rather than evidence.
One thing that superfuits do have in common, however, is a high ORAC value.
The Oxygen Radical Absorbance Capacity (ORAC) assay was developed to directly test the antioxidant capacity of biological samples. There are however many different tests of antioxidant capacity that have been developed and utilized, each with various shortcomings. As the developers of the ORAC assay state, a “‘battery’ of measurements are necessary to adequately assess oxidative stress in biological systems.” (2) Systemic oxidative stress must be interpreted in context of the dynamic system in which it is regulated; increases or decreases in total antioxidant capacity is not necessarily beneficial or harmful, dependent on context. In this sense we must be cautious when interpreting results of studies using in vitro assays to measure antioxidant capacity, and ensure we can causally link them with appropriate outcomes relevant to health.
One dogmatic and frequent commercial claim is that free radicals are a cause of ageing. This is the basis of the outdated systemic oxidative stress (or free radical) theory of ageing. If this were the case, manipulation of endogenous antioxidant enzymes should effect lifespan. However (now over) 18 genetic manipulations in rodents of endogenous antioxidants suggest otherwise (1). There is suggestion on multiple lines of evidence that mitochondrial antioxidant enzymes influence lifespan, but this would not be represented by ORAC, nor likely influenced by superfruits, at least greater than any “normal” fruit. Thus, claims that superfruits will slow the ageing process are false.
Systemic oxidative stress still may influence various disease risks, independent of the ageing process itself. This is often described as “healthspan” (rather than lifespan) in the literature. Indeed, diets rich in fruit and vegetable intake are correlated to many positive outcomes against many disease risks, and it has been confirmed that an increase in fruit and vegetable intake increases the ORAC value of their blood plasma (2). But can the increased antioxidant capacity completely explain the benefits of fruits and vegetables?
There have been a number of rodent studies using several different fruit or vegetable extracts that have examined their effects on brain and behavioral function (3). These include strawberry, spinach, blueberry, cranberry, and grape extracts. Interestingly, even with equivalent ORAC values, the fruits do not equally effect the age related tests or oxidative challenges that the animals are subjected to. As noted by the authors, “…it seems that antioxidant activity alone was not predictive in assessing the potency of these compounds against certain disorders affected by aging. In fact, oxidative stress markers (as measured by DCF fluorescence and glutathione levels in the brain) were only modestly reduced by the diets, suggesting that these fruit and vegetable polyphenolics possess a multiplicity of actions, aside from antioxidative, and that differences in the polyphenolic composition of these extracts could account for the positive effects observed.”
This suggests that we shouldn’t only look at antioxidant measure as a predictor of health outcomes. In these studies, this is true for ORAC values, and recall that this is what superfruits are marketed by.
Summarized in the paper (3), polyphenolic compounds have been demonstrated to have many other properties apart from antioxidant effects, including: anti-inflammatory, neuronal signaling, calcium buffering, enhancing neuroprotective stress shock proteins, reduction of stress signals, enhancement of hippocampal plasticity, neurogenesis, improvements of spatial memory (likely mediated by an increase in IGF-1). Besides having direct antioxidant potential, they also can upregulate certain endogenous antioxidant enzymes, as well as modulating other signaling pathways at the transcriptional level. Several transgenic models have shown that berry extracts do indeed seem to effect learning and memory processes through signaling rather than through an attenuation of oxidative stress. Further studies will need to elucidate in which ways polyphenols influence various processes the most. A thorough dissection of potential mechanisms is available here.
These findings are being translated to humans with preliminary studies. For example, 1 study using Concord grape juice and 1 with blueberry juice have found a positive effect on measures of cognitive function in older adults. Though these could perhaps be labeled “super”fruits by their ORAC values, they are inexpensive alternatives to the exotic “in” fruit marketers that fill your stomach with false claims while emptying your wallet.
In addition, there have been studies in humans using “normal” fruit juices or extracts on biomarkers of other disease risks. Pomegranate juice for example has been studied in diabetics, in hypertensive subjects, for erectile dysfunction, in subjects with prostate cancer, and more with some positive effects. In other areas, wines, beer, teas, coffee, and other juices correlate with certain health measures, though more interventional studies are needed for each. Not all juices, like cranberry juice in this study, with high in vitro antioxidant potency are able to increase in vivo antioxidant status in humans, though it does in rats. Extensive metabolization of polyphenols make it necessary to measure concentrations in the body to ensure it is physiologically and clinically relevant. Some authors even suggest that uric acid, and not so much flavonoids themselves increase antioxidant capacity in vivo. These findings further the need for in vivo, human trials on fruit juices before their antioxidant potential are bragged about.
As stated previously, multiple antioxidant tests should be performed to more accurately estimate antioxidant capacity, because of shortcomings of each as discussed in (2). This is exactly what Seeram et al. (4) did on pomegranate juice, red wine, Concord grape juice, blueberry juice, black cherry juice, acai juice, cranberry juice, orange juice, iced green tea, iced black tea, iced white tea, and apple juice; each was subjected to 4 different assays of antioxidant potency, as well as an antioxidant functionality test. As stated by the authors, “…antioxidants respond to different reactive species in different tests, which is partially attributed to multiple reaction mechanisms and reaction phases.” The ORAC assay itself yielded the following order of potency: Concord grape juice, red wine, pomegranate juice, black cherry juice, blueberry juice, acai juice, cranberry juice, orange juice, iced tea beverages, and apple juice. When the 4 assays are combined into 1 index, the order of potency was as follows: pomegranate juice, red wine, grape juice, blueberry juice, black cherry juice, acai juice, cranberry juice, iced tea beverages, orange juice, and apple juice.
As evidenced by the study, different assays can yield different results, and the authors note that ORAC “can have significant internal variabilities.” They also raise great points with: “because in vitro results are not necessarily translated into in vivo effects, issues such as the bioavailability and metabolism of phenolic compounds should be taken into account in the overall evaluation of the impact of phenolic/antioxidant-rich” foods on human health.”
Also take note that acai failed to beat most beverages in any assay or when combined. In fact, many “normal” fruits contained a higher antioxidant capacity, which in itself shows that recent marketing trends are not based on proper scientific evidence.
Potential risks of superfruit products
Like any nutrient, overconsumption carries certain risks as well. Skibola and Smith speculated on this in which their abstract summarizes well: “Plant flavonoids are common dietary components that have many potent biological properties. Early studies of these compounds investigated their mutagenic and genotoxic activity in a number of in vitro assays. Recently, a renewed interest in flavonoids has been fueled by the antioxidant and estrogenic effects ascribed to them. This has led to their proposed use as anticarcinogens and cardioprotective agents, prompting a dramatic increase in their consumption as dietary supplements. Unfortunately, the potentially toxic effects of excessive flavonoid intake are largely ignored. At higher doses, flavonoids may act as mutagens, pro-oxidants that generate free radicals, and as inhibitors of key enzymes involved in hormone metabolism. Thus, in high doses, the adverse effects of flavonoids may outweigh their beneficial ones, and caution should be exercised in ingesting them at levels above that which would be obtained from a typical vegetarian diet. The unborn fetus may be especially at risk, since flavonoids readily cross the placenta. More research on the toxicological properties of flavonoids is warranted given their increasing levels of consumption.”
The quote “the dose determines the poison” is relevant to this issue. Is a high intake of fruit juices or supplements, super or normal, harmful to health? Hormetic theory suggests that noxious phytochemicals that protect plants promote cellular stress responses at the subtoxic levels we consume them at. At normal concentrations, this is good, but when unnaturally high, it is clear from the in vitro data that they have different effects. The in vivo implications aren’t yet well understood, so until then, fruit intake or small amounts of fruit juice at amounts that are obtainable through diet seem important for healthy ageing.
Like any supplement in a largely unregulated industry, there is a risk that a product can contain something not on the label. There is no exception for acai products.
In addition to potential health risks, many scams exist on superfruit related products. Caveat emptor.
My suggestions? Choose several fruits or (100%) fruit juices (but don’t drink too much; studies I have looked at tend to use no more than a few cups) and consume on a (semi-)consistent basis. It is likely in my opinion that we will find although different fruits have slightly different effects on disease outcomes in humans, many share common mechanisms. There is no need to choose specific fruits over another if you are in a healthy condition.
A limited number of fruits have been examined for their antioxidant potency with multiple assays, thus the most common fruits that have been looked at are not necessarily the best. We should not be tailoring diets at this point with specific fruits unless you accept the risks of our limited understanding of specific fruits on older populations or in diseased subjects.
The bottom line:
The ORAC assay, like any has its limitations. Multiple assays should be conducted to determine antioxidant potency of a fruit. Other considerations include absorption, metabolization, distribution, among others. Superfruit products simply take advantage of consumer and marketing trends. Even some of the fruits (like acai) that are claimed to have high antioxidant abilities are no better, and worse than some common fruits. We should be more cautious when supplementing polyphenols in amounts higher than achievable through diet, because of potential negative effects.
1. Pérez VI, Bokov A, Van Remmen H, Mele J, Ran Q, Ikeno Y, & Richardson A (2009). Is the oxidative stress theory of aging dead? Biochimica et biophysica acta, 1790 (10), 1005-14 PMID: 19524016
2. Prior RL, & Cao G (1999). In vivo total antioxidant capacity: comparison of different analytical methods. Free radical biology & medicine, 27 (11-12), 1173-81 PMID: 10641708
3. Shukitt-Hale B, Lau FC, & Joseph JA (2008). Berry fruit supplementation and the aging brain. Journal of agricultural and food chemistry, 56 (3), 636-41 PMID: 18211020
4. Seeram NP, Aviram M, Zhang Y, Henning SM, Feng L, Dreher M, & Heber D (2008). Comparison of antioxidant potency of commonly consumed polyphenol-rich beverages in the United States. Journal of agricultural and food chemistry, 56 (4), 1415-22 PMID: 18220345