DAIRY, BEANS, AND HEALTH
An interview with Gerd Bobe, Ph.D.
Q. You were born and raised in Europe. What brought you to the United States?
A. I was raised on a farm in western Germany. Originally, I wanted to study abroad for one year. When I talked to students who had studied abroad, they told me that one year wouldn’t be enough to learn about American culture and research. So I applied for a Master’s degree, met my wife, earned my Ph.D., and stayed here.
Q. Is there much difference between the research environment in Europe and in the United States?
A. There were many differences when I left Europe in the early 1990s. For example, less funding was available for research in agriculture and animal science.
Q. You earned a Ph.D. in animal nutrition from Iowa State University. Do you think that your early exposure to farm life stimulated your interest in animal nutrition?
A. Definitely. I have an older brother who did all the outside work, while I helped with the animals. Taking care of animals has always been very important to me.
Q. Your initial research concerned the fatty acid and protein composition of milk in cows and dairy products. What did you learn about that relationship?
A. In a series of studies, I showed that milk protein and fatty acid profiles can be altered by the cow’s diet and breeding.
Q. How does the cow’s diet affect the quality of dairy products like milk and butter?
A. I demonstrated in a series of experiments that the cow’s diet can improve the fatty acid profile and the textural properties of milk and dairy products.
Q. How does changing the cow’s diet by including certain grains or nuts influence things like butter?
A. Feeding cows oil seeds that are rich in polyunsaturated fatty acids increases the proportion of unsaturated fatty acids and decreases the proportion of saturated fatty acids in dairy products.
Q. Were you mainly interested in the health effects of the dairy products, not their palatability?
A. The main focus was to improve the fatty acid profile and the nutritional properties of dairy products for human consumption.
Q. Do you think that the routine use of hormones in dairy cows or cattle poses any serious threat to human health?
A. I’m not aware of any detrimental effects on human health.
Q. What about the use of antibiotics to spur growth and to protect cows and cattle from infection? Do you think that has any health consequence for people who consume those dairy or beef products?
A. Again, I’m not aware of any detrimental effects on human health when antibiotics are used according to their labeled directions.
Q. Does cow’s milk contain partially hydrogenated or trans fat and, if so, does that have consequences for human health?
A. The milk of dairy cows contains trans fatty acids; however, consumption of trans fatty acids from ruminant sources has not been associated with detrimental effects on human health, unlike trans fatty acids from the industrial partial hydrogenation of vegetable oils.
Q. What is conjugated linoleic acid, or CLA? Does it have any special health benefit?
A. Conjugated linoleic acid is a group of isomers of linoleic acid. Isomers are compounds that have the same chemical makeup but different structures. Most research has been done on cis-9, trans-11 linoleic acid and trans-10, cis-12 linoleic acid. I was involved in a study that examined the effect of these isomers on gene expression of the corpus luteum in the ovaries of cows and reported that both isomers downregulated the gene expression of cyclooxygenase 2 (COX-2). Inhibitors of COX-2 have been shown to inhibit inflammation and decrease the risk of many chronic diseases.
Q. How does CLA occur in dietary sources?
A. Cis-9, trans-11 linoleic acid is predominantly synthesized in tissues from trans-11 linoleic acids by delta-9 desaturases. Trans-10, cis-12 linoleic acid and the remaining proportion of cis-9, trans-11 are synthesized by microorganisms in the cow’s rumen from linolenic acid and linoleic acid.
Q. You’ve also looked into the relationship between selenium status and immune function in sheep. Does that have relevance to people?
A. The objective of the studies has been to examine the effect of selenium source (inorganic sodium selenite versus organic selenium yeast) and dosage (regular versus supranutritional—higher than what is usually consumed dietarily—dosage) on selenium status, performance, and health of ewes and their progeny. The studies are still ongoing.
Q. A lot of your research has focused on the effects of flavonoids, which are polyphenolic pigments from plants, on intestinal cancer in mice, the risk of pancreatic cancer in human smokers, and the recurrence of colorectal polyps in the Polyp Prevention Trial. What led to your interest in flavonoids?
A. In cell culture and animal models for chronic diseases, flavonoids exhibit biochemical properties beneficial for the prevention of multiple chronic diseases, including cancer. Looking at the effect of flavonoids on cancer risk in epidemiological studies was the logical next step.
Q. What was the Polyp Prevention Trial?
A. The Polyp Prevention Trial (PPT) was a large, multicenter, randomized four-year nutritional intervention trial in the early 1990s that evaluated the effects of promoting a high-fiber, high-fruit and -vegetable, low-fat diet on the recurrence of any or advanced colorectal adenoma.
Q. What was the main outcome of that study?
A. The main outcome was that the intervention and control group did not differ in recurrence of any or advanced adenoma. However, strict adherence to a low-fat (≤ 20% of energy intake), high-fiber (≥ 18 grams per 1,000 kcal of energy), high-fruit and -vegetable diet (≥ 3.5 servings per 1,000 kcal) was associated with a 35% and 56% decrease of any and advanced colorectal adenoma recurrence, respectively.
Q. Did they measure oxidative stress or inflammation in those participants?
A. Several genetic and blood markers of metabolic syndrome and inflammation were measured. We identified several biomarkers that were modified by diet and/or predicted risk of adenoma recurrence.
Q. Do we know that flavonoids in food help protect against polyps or colon cancer?
A. In the PPT, a flavonol-rich diet was associated with a decreased risk of advanced colorectal adenoma recurrence. Flavonols are a subclass of flavonoids.
Q. Since absorption of flavonoids into the blood stream is quite limited, and they are very quickly metabolized once absorbed, is their beneficial effect due, then, to a local effect in the colon?
A. This is an area of active research—we did not examine that.
Q. What compounds are synthesized by gut microbes that might have beneficial effects?
A. Butyrate is one compound that has been proposed to have beneficial effects. There are probably many more compounds that have beneficial effects—this is a new, rapidly growing research area. We still have a lot to learn.
Q. What is butyrate?
A. Butyrate is a four-carbon, short-chain fatty acid produced by intestinal microorganisms.
Q. How do flavonoids compare with other dietary factors in protecting against polyp formation or colon cancer?
A. In the PPT, a high-dry bean diet and a flavonol-rich diet were associated with decreased advanced adenoma recurrence.
Q. Do different types of flavonoids have different health effects?
A. Based on results from cell culture studies and animal models of chronic diseases, individual flavonoids differ in their action on biochemical pathways. In the PPT, only the consumption of the flavonoid subgroups flavonols and, to a smaller extent, isoflavonoids was associated with decreased advanced adenoma recurrence.
Q. Is it possible to estimate total flavonoid intake from the diet?
A. It is difficult to accurately estimate flavonoid intake from the diet because of limitations in flavonoid databases from foods, variations in the food quantities of recipes, and variability of flavonoid content due to the climatic, growing, soil, and harvesting conditions of plants, and storage conditions and preparation of foods.
Q. Why are flavonoids synthesized in plants? What function do they perform?
A. Flavonoids have multiple functions in plants. It has been proposed that flavonoids and their metabolites have roles in UV protection and signaling in symbiosis, as well as acting as chemical messengers to regulate physiological processes, as pigments to attract pollinator animals, and as defensive compounds against pathogens.
Q. Flavonoids in tea have been found to inhibit lesions in the rat colon induced by dietary mutagens. Do flavonoids also protect against esophageal cancer?
A. There are two histological types of esophageal cancer—esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC)—that differ in their etiology. EAC is associated strongly with gastro- esophageal reflux disease and obesity, while ESCC is associated strongly with tobacco and alcohol consumption. I was involved in a population-based, case-control study of white and black men in the U.S. that examined the effect of flavonoid consumption on the risk of EAC and ESCC. Overall, consumption of total flavonoids had little protective effect in this population of heavy smokers and drinkers; however, there was some suggestion that foods rich in the flavonoid subgroup anthocyanidins may be protective in EAC and that isoflavonoid-rich foods may be protective in ESCC.
Q. You also investigated the role of lignans, legumes, beans, and sugar on colon cancer. What did you find?
A. Lignans are diphenolic compounds present in the structural portion of plants, which are partially or fully converted by the intestinal microorganisms to enterolactone and enterodiol. In the PPT, individual and total lignan intake was not associated with colorectal adenoma recurrence; however, high-lignan intake was associated with the increased risk of any adenoma recurrence in women and in individuals with saturated fat intake below or equal to 18.3 grams per day.
Q. What about legumes and beans?
A. In the PPT, a high-dry bean diet was associated with a decreased risk of advanced colorectal adenoma recurrence. The results from the PPT were followed up by the Legume Inflammation Feeding Experiment (LIFE), a randomized, crossover feeding study of a legume-enriched (250 grams per day) diet among men under conditions of weight maintenance. The main study was followed by a third, optional four-week period, which encouraged weight loss. Participants lost on average 4.4% of their body weight during the weight-loss phase and improved biomarkers of metabolic syndrome and inflammation.
Q. What about sucrose intake?
A. Using a mouse model of colon cancer, we reported that sucrose compared to cornstarch consumption increased tumor number, serum glucose and insulin concentrations, and body weight in those mice.
Q. Does a low glycemic diet that emphasizes legumes improve blood lipid profiles?
A. During the four weeks on the high-legume, high-fiber, and low-glycemic index diet in the LIFE Study, total and low-density lipoprotein (LDL) cholesterol concentrations during the weight-maintenance phase decreased by 10% and 11%, respectively, and during the weight-loss phase by 13% and 16%, respectively. In addition, total trigly- ceride concentrations decreased on the high-legume diet by 15% and 28% during the weight-maintenance phase and the weight-loss phase, respectively.
Q. How does that diet affect insulin resistance and inflammation?
A. During the four-week weight-loss phase, glucose and insulin concentrations dropped by 6% and 14%, respectively. In addition, concentrations of the inflammatory markers, C-reactive protein and soluble TNF receptor 1, decreased during the weight- maintenance phase and the weight-loss phase.
Q. What kinds of beans were used in that diet?
A. The high-legume diet contained approximately 250 grams or 1.5 cups of legumes a day. The legumes were of the Phaseolus vulgaris species and included navy, pinto, kidney, lima, and black beans.
Q. Based on your research in this area, would you make any special dietary recommendations for people who are trying to manage weight and help prevent age-related disease?
A. The results of the PPT and the LIFE study are encouraging. Further research needs to be done to validate those findings before dietary recommendations can be made. Personally, I increased my consumption of beans, fiber, fruit, and vegetables over the last few years.
Q. What are you currently working on?
A. I work on identifying metabolic pathways and biomarkers that are modifiable by legume and flavonol intake and can predict cancer risk.
Q. And that, of course, has relevance not only to cancer but also to cardiovascular disease and diabetes?
Q. Where is your research headed?
A. My research is headed toward personalized cancer and disease prevention. I will use an “omics” approach—genomics, proteomics, metabolomics—to look at genes, proteins, metabolites, and other substances in human intervention trials to identify subpopulations that most likely benefit from a particular diet.
Q. How do you like the Linus Pauling Institute’s new building?
A. It is a dream come true!
Q. Does it meet all your research needs?
A. Definitely! It is great to work in close proximity to a group of very talented and highly successful researchers, which makes your own work so much better.
Q. Do you like living in Oregon?
A. Yes. We are close to the coast and to the mountains, and the rain in the winter doesn’t bother me. Corvallis reminds me of where I was raised in Germany.
Q. What do you like to do in your free time?
A. I love to spend time with my seven-year-old daughter. Family is very important to me.
Last updated May 2012