The Indisputable Benefits of Largely Plant-based Diets

[caption id="attachment_2785" align="alignleft" width="531"] Photo: Loreto di Cesare[/caption]In a recent US News and World Report on the Healthiest Diets, the Mediterranean diet was selected from 41 competitors as the 2019's best overall diet. It is important to point out that it is the traditional version of Mediterranean diet that stands out in its health-promoting effects. Many changes to this dietary pattern have occurred since it first captured the attention of diet experts in the 1960s, in particular an increase in portion sizes, red meat and animal fat ingredients, and in processed foods. Many areas of Italy do not adhere to the original formulation, with the Parma region being a good example where the famous ham and cheese are synonymous with the region. These changes in the Mediterranean diet in Italy over the last 50 years are reflected in the increase in obesity, type 2 diabetes and metabolic syndrome, with Italian children now having one of the highest obesity rates in the Western world While the choice of the traditional Mediterranean diet as the best overall diet is not surprising to many people following evidence-based dietary recommendations, the report was interesting in terms of the runner ups in the ranking, such as the DASH, MIND, Ornish, Flexitarian and Nordic diets: All these study-supported, health-promoting and disease-fighting diets require the use of minimally processed foods and focus on plant-based products, such as fruits, vegetables, beans, lentils, whole grains, nuts and seeds. Also, these diets do not require the complete elimination of occasional consumption of animal products, or of indulgences like chocolate, or small deserts, making it easier to adhere to them. What is the magic behind the health-promoting effects of these diets? Plant-based foods are the primary source of dietary fiber, which amongst other benefits assures a healthy and diverse gut microbiome, in particular if the source of the different types of fiber is a high variety of plants and vegetables. Plant- based foods are also the primary source for vitamins, antioxidants and polyphenols, the latter coming primarily from dark colored berries, olive oil, coffee, dark chocolate, spices and red wine. The latest research has shown that only a small fraction of these large plant-derived molecules can be absorbed in the small intestine as antioxidants, while the great majority serve as substrate the gut microbiota, so called prebiotics. Once they reach the large intestine, polyphenols not only change the relative abundances of…

Microbes Adapt to Their New Environment Along with Their Immigrant Hosts

A recent article published by Dan Knights’ group at the University of Minnesota and reported in the journal Cell reports that gut microbial composition and diversity changed within months in immigrants from rural Asian environments to the US. The authors’ key findings were: Immigration to the US from rural regions in Asia is associated with loss of gut microbial species, diversity and loss of bacterial enzymes associated with plant fiber degradation Bacteroides strains displaced fiber-digesting Prevotella strains according to time spent in the USA Loss of diversity increased with obesity and was compounded across generations “People began to lose their native microbes almost immediately after arriving in the U.S.,” Knights said when interviewed by The Washington Post. “The loss of diversity was quite pronounced: Just coming to the USA, just living in the USA, was associated with a loss of about 15 percent of microbiome diversity.” Interestingly, the children of immigrants had another 5 to 10 percent loss of diversity. Knights and his colleagues examined the relative abundance and diversity of gut microbes and their gene content in stool samples from more than 500 immigrant women from rural areas in Asia, the Hmong and Karen people. To get a snapshot before and after arrival in the US, researchers also took microbiome samples from 19 Karen women before their departure and after their arrival. The scientists compared all of these microbiomes with those of 36 European Americans born in the United States. The dominant species in the gut of immigrants changed from strains of a group of bacteria called Prevotella to a group called Bacteroides. The genus Prevotella belongs to the taxa Bacteroidites which together with the taxa Firmicutes makes up the majority of gut microbes in the human GI tract. Similar differences in gut microbial taxa between the remnants of hunter gatherer populations in Africa (Hadza) and South America (Yanomami), and populations living in industrialized countries, in particular in North America, Europe and Australia have previously been described (Smits et al. Science 357, 2017; De Filippo, PNAS 2010). Industrialized populations have microbiotas that are dominated by Bacterioidites, whereas traditional populations across the African, Asian, and South American continents, which include a range of lifestyles from rural agriculturalists to hunter gatherers, have microbiotas that are in part distinguished by their abundances of Prevotella taxa, just like in the Knight’s study (Smits et al. Science). [caption id="attachment_2754" align="alignleft" width="300"] Village Africa Burkina…

Can the Iceman Tell Us Something About the Healthiest Diet?

The “Iceman” or “Ötzi” refers to an individual whose mummy was found about 10 years ago in the receding glaciers of the Ötztal Alps a mountain range in the central Alps between Austria and Italy. His well preserved body has been stored in a cooling chamber of the Archeology Museum in Bolzano, Italy, and is probably the most thoroughly investigated individual from the Neolithic period. Can the stomach contents of this individual reveal something about the preferred diet of people transitioning from a hunter gatherer to an agrarian lifestyle, and the associated health benefits? To answer this question, investigators have examined the stomach contents of this 5,300-year old European glacier mummy who according to the latest forensic studies was killed by an arrow shortly after enjoying his last meal. The study revealed that the Iceman had a remarkably high proportion of fat in his diet, supplemented with fresh or dried wild meat and ancient grains. An earlier study had demonstrated that the gut microbial composition of the Iceman was more similar to microbiomes of agrarian societies (and of primates), suggesting a predominantly plant based diet with an occasional treat of wild game. Do we have any evidence for the health benefits of this ancient diet? The investigators were surprised of the large amount of animal fat found in the person’s stomach. The investigators asked: “Did he load up on fatty meat to meat the caloric needs of roaming in the extreme alpine environment in which he lived and where he was found at 3,210m above sea level?” On the other hand, the intake of animal adipose tissue fat has a strong correlation with increased risk of coronary artery disease. There was evidence on computer tomographic scans of the Iceman that he had major calcifications of his major blood vessels consisting with advanced atherosclerotic disease state, a surprising finding in an individual who likely got regular vigorous workouts climbing up and down the mountains in his backyard. He was in his 40s, the average life expectancy of people of his time, half of our current life expectancy. Obviously, the study only provides a snapshot of dietary habits of this time, and tells us little about the average intake of different types of food and the relative proportion of carbs, protein and fat. However, in view of the presence of grains and carbohydrates in his stomach and the composition of his gut…

Lessons Learned from the Gut Microbiome of Hibernating Brown Bears

Obesity and compromised metabolic health are often thought to be closely linked. However, a study by Fredrik Baeckhed’s group at the University of Gothenburg suggests that this is not necessarily the case – at least in brown bears! (1) By studying body weight and the gut microbiota in brown bears both during the summer and during the winter period - when these animals go into a 6 months hibernation period - they identified major differences in the diversity and relative abundances of certain gut microbiota. During the summer the bears overeat and dramatically gain body weight, while during the prolonged fasting period in winter they lose all the excess weight. The most fascinating aspect of this study was that despite their “summer obesity” the bears did not develop the negative metabolic changes including insulin resistance and diabetes known as metabolic syndrome, a metabolic dysregulation which has shown a dramatic increase in North America and other developed countries. Looking for a possible role of the gut microbiome in these seasonal metabolic changes, the investigators looked at the bears’ gut microbes and metabolites. Surprisingly, during hibernation there was a reduction in diversity and reduced levels of certain taxa, in particular Firmicutes and Actinobacteria, and increased levels of Bacteroidetes. Transfer of the stool of bears obtained during different seasons into germ free mice (mice without their own gut microbiome) mimicked some of the metabolic findings of the bears, clearly implicating a role of the microbiome in the seasonal metabolic variations. The three microbial taxa that showed seasonal variations in the bears make up the majority of the human gut microbiota, and changes in their relative abundance in the gut have previously been shown by Ruth Ley and coworkers in obese subjects. (2) In their study, they found that the relative abundance of Bacteroidetes increases while that of Firmicutes decreases as obese individuals lose weight on either a fat- or a carbohydrate-restricted low-calorie diet. The increase in Bacteroidetes was significantly correlated to weight loss but not to total caloric intake. In a study by Peter Turnbaugh and coworkers, the investigators showed that when ‘obese microbiota’ were transplanted into the gut of mice without their own microbiota (so called germ free mice) they showed a significantly greater increase in total body fat than mice colonized with the ‘lean microbiota’. Their results suggested that an “obese microbiome” has an increased capacity to harvest energy from the…

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