Friday, July 31, 2015

Yogurts, Cheeses & Beyond - A Comprehensive Review of the Potential Health Benefits of Fermented Dairy Products

Yogurt does not have to be served this way to be healthy, but I bet many of your friends and relatives would be amazed and much more likely to pass on the cream cake or tiramisu if the option was an appetizing dessert like that.
In a world where being vegan is "the new sexy" and eating animal products "the new smoking", dairy has lost much of its former appeal. I mean, we all remember how the literal "glass of milk" has been marketed as a daily health booster, right? Well, times have changed and that despite the fact that an impartial review of the evidence suggests more benefits than downsides to dairy consumption. Specifically fermented dairy, first and foremost yogurt, but also cheese can, and in the case of yogurt maybe even should be part of your of your diet. And that's not just because both are an often forgotten, but essential part hailed "Mediterranean diet" (Vasilopoulou. 2013). The same diet of which recent studies say that it's associated w/ a -30% reduced CVD risk (Estruch. 2013).
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How's that? Well, cheese may be full of saturated fat and cholesterol. In controlled trials, however, even high fat cheese has - in contrast to butter, for example (Hjerpsted. 2011) - no or even beneficial effects on the total and LDL cholesterol levels of otherwise healthy individuals. In addition, real dairy cheese has been found to have neutral effects on body weight when it is consumed as part of an otherwise healthy diet. Some traditional types of cheese even share the anti-hypertensive effects of yogurt, which is still the real star among the fermented dairy products. A star that has been shown to prevent weight gain, reduce cholesterol and more meaningful makers of heart disease risk, to improve glycemia, and to prevent the development and/or progression of type II diabetes in both experimental and observational studies (Tholstrup. 2006; Nestel. 2008; Mozaffarian. 2011, Tapsell. 2015).
Figure 1: A study comparing the effects of getting 13% of one's total daily fat intake from cheese vs. butter on the blood lipids in healthy men and women shows increases in TC and LDL only with butter (Hjerpsted. 2013). In contrast to the total and LDL cholesterol levels, the total / HDL cholesterol ratio wasn't affected sign. by butter though. You can thus expect both forms of high fat dairy having negligible cholesterol mediated effects on the heart health of healthy indiv.
In short, the existing scientific evidence leaves little doubt that yogurt is, maybe next to whey (learn why), the star among the dairy based health foods. Part of its beneficial effects are probably mediated by its ability to improve integrity of our digestive tracts and thus to prevent the influx of pro-inflammatory, obesogenic, and pro-atherogenic endotoxins into the bloodstream. With it being available for almost 10,000 years, yogurt is thus the first and oldest "functional food" to act on the recently discovered link between "leaky gut", obesity and cardiovascular disease (Lam. 2011).
Figure 2: Proposed mechanisms by which yogurt consumption exerts beneficial health effects (Marette. 2015)
Some scientists like Marette & Picard-Deland even go so far as to argue that an early introduction of yoghurt into the diets of children is vital to establish a microbial community that supports long-term health. And while Taspell et al. are right to highlight that "[m]ore research is needed" (Tapsell. 2015). There's little doubt that "yogurt can deliver essential nutrients with high bioavailability and relatively low energy density" (ibid).
If the caloric content is controlled, the consumption of a high amount of dairy products (both fermented and non-fermented) is associated w/ sign. greater weight and fat loss - specifically unhealthy trunk fat (Zemel. 2015).
Simply adding yogurt or fermented dairy on top of an unhealthy diet is not going to cut it: People often fail to understand that "superfoods", no matter how "super" they are, can't work their weight loss or health magic if they are simply added on top of one's habitual diets. It is thus not surprising that the addition of yogurt and other fermented dairy products to the Western diet will not yield any significant health benefits if it does not replaces other, less healthier foods. If the energy intake is controlled for, as it was the case in a 2004 study by Zemel et al. higher dairy intakes are however - independent of their calcium content - associated w/ sign. greater weight & fat loss (s. left Figure)
The fact pertinent trials still show ambiguous results, when it comes to the effects of yogurt on body weight and composition (Chen. 2012) is mostly a results of the study designs which usually require subjects to simply increase their intake of dairy products, in general, or yogurt, in particular. As Taspell (2015) points out in a recent review this is a problem "if the energy content of the diet is not managed, particularly with high-fat varieties and with added ingredients such as sugar" (ibid). If it is managed, as in habitual consumers, though, high(er) yogurt intakes have been shown to be associated...
  • Prevalent Nutrient Deficiencies in the US: More Than 40% are Vitamin A, C, D & E, Calcium or Magnesium Deficient and >90% Don't Get Enough Choline, Fiber & Potassium | read more
    with higher scores for the Dietary Guidelines Adherence Index (DGAI) and higher intakes of key micronutrients, as well as significantly higher potassium and fiber intakes - two nutrients the average Westerner usually doesn't get enough of (Wang. 2013)
  • with reduced weight gain in a large US cohort study that tracked the food intake and weight development of 22 557 men and 98 320 women for four years; with R = -0.89 the correlation is similar to the one for the recommended amount of physical activity vs. being sedentary and thus nothing you should ignore as being practically irrelevant
  • with reduced inflammation as measured by C-reactive protein, IL-6 and TNF-a in the ATTICA study that involved 3042 healthy Greek adults for whom only 8 servings of dairy products, in general (full fat and low fat!), were linked with already significant reductions in inflammation; since a greater proportion of the cohort reported consumption of fermented dairy foods such as feta cheese (93%), hard yellow cheese (92%) and low-fat yogurt (50%) compared to low-fat milk (46%), we can yet safely assume that many of these anti-inflammatory benefits were actually due to fermented dairy products
  • with reduced type II diabetes risk (-12% or both yogurt and cheese) in the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct Study (Sluijs. 2012);
    Table 1: HRs for risk of type 2 diabetes associated with the substitution of yoghurt (137 ga) for snacks and desserts: EPIC-Norfolk study (n=4,127 | O'Connor. 2014)
    with 28% reduced diabetes risk the results of the EPIC-Norfolk cohort study in the UK were even more impressive (O’Connor. 2014); as you can see in Table 1 the results of this study do yet also underline that the benefits will occur only if yogurt replaces other, less healthier ingredients of ones diet.
Other studies detected significantly lower common carotid artery intima-media thickness (CCA-IMT) in older, female Australian yogurt enthusiasts who consumed only 100g of common yogurt per day (CCA-IMTadj = -0.023 mm, P< 0·003 | Ivey. 2011). And as far as cheeses are concerned evidence from studies like Struijk et al. (2013) which found significant negative associations between cheese intake and the 2h-post prandial glucose levels, a marker that's highly predictive of one's future diabetes risk (Struijk. 2013) and a much better indicator of diabetes-related CVD risk than fasting glucose (Lithell. 2001), would suggest that the existing link between higher cheese intakes and diabetes may be mediated by the complex food matrices in which cheese appears in the Western diet: Cheeseburger, pizza, etc. In the standard Western diet, cheese is always added on top of other (usual junk) foods, which is much in contrast to the way it is consumed in the initially reference Mediterranean diet. 
Kids who drink more milk, tend to be leaner... and that despite (?) the fact that this stuff comes out of an animal and is full of bad cholesterol and fat - outrageous? Not exactly... more!
Does it have to be yogurt with patented probiotics? While some studies like Asemi et al. show benefits of one or several of the myriad of patented yogurt strains, most of the existing evidence suggests that regular yogurt which will also contain sign. amounts of "good" bacteria will have effects that are very similar to those of the expensive "functional foods". I mean, there's a reason yogurt and other fermented dairy foods have been part of the human diet ever since 10 000–5000 BC when we first domesticated milk-producing animals (cows, sheep, and goats, as well as yaks, horses, buffalo, and camels | Moreno. 2012).

For certain parts of the population (like people with high cholesterol, for example), certain starter cultures may yet have sign. advantages - which of the various currently available cultures will have the greatest health impact does yet still have to be elucidated. Next to the starter cultures, the protein content of the end product may be another important thing to keep in mind. Douglas et al. (2013), for example were able to show that Greek yogurt with 24g of protein per 250ml serving has a significantly higher satiety effect than yogurt with lower protein content.
Now this wouldn't be a SuppVersity article if it would rely exclusively on observational evidence. It is thus important to point out that Nestel's 2013 three-week crossover study comparing the effects of dairy foods categorized as low-fat (milk/yogurt), fermented (yogurt/cheese) or non-fermented (butter/cream/ice cream) confirmed that the concentrations of inflammatory markers like IL-6 were significantly lower on the fermented dairy diet than on the non-fermented dairy diet (P < 0.05).
Table 2: While everyone appears to believe that eating cheese was consistently associated with increased CVD risk, the majority of the existing studies shows no sign. association between cheese consumption and cardiovascular disease - especially when the data is adjusted for other dietary factors (summary from Elwood. 2010).
Clinical trials like Nikooyeh, et al. (2011) or Neyestani (2012) show improvements in glycemia, inflammation and adiponectin in type II diabetics and suggest that yogurt may be an ideal vehicle to increase our daily vitamin D3 intakes (by fortification).

Other researchers have been able to show that the consumption of a yogurt snack in the afternoon has potent beneficial effects on appetite control and eating initiation in healthy women (Ortinau. 2013; Douglas. 2013). Similar, yet in many cases more pronounced benefits have been observed in animal studies - studies that also indicate that yogurt exerts, next to its metabolic effects, direct inhibitory effects on colon cancer development and progression, too (de LeBlanc. 2004). All that doesn't negate the need for "[m]ore randomised controlled trials" but as Tapsell highlights in her recent review "the picture [which shows fermented dairy as a health food] is becoming clearer" (Tapsell. 2015). 
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So what? While it is obvious that yogurt and other fermented dairy products alone won't solve the Western diabesity crisis. It is unquestionably noteworthy that only 6% of the population in the US or Brazil, where the diabesity epidemic has really been taking off lately, consume yogurt on a daily basis.

As Fisberg et al. (2013) highlight in their review of the history of yogurt, this "represents a missed opportunity to contribute to a healthy lifestyle, as yogurt provides a good to excellent source of highly bioavailable protein and an excellent source of calcium as well as a source of probiotics that may provide a range of health benefits" (Fisberg. 2013).

One thing you must not forget, though, is that all the beneficial effects of yogurt and other fermented dairy products can take full effect only if they are integrated into an overall healthy diet. If you do it like my grandma and add one of those overpriced probiotic drinks to your otherwise pro-inflammatory breakfast, you may upset your knowledgeable grandson, but won't do much for your metabolic and overall health | Comment on Facebook!
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