My research mainly focuses in the area of dietary intakes, lifestyle behavior and disease conditions including hypertension, weight control and most recently prostate cancer. I was a key member of the team that developed the DASH dietary pattern initially and has studied this dietary pattern including and beyond its blood pressure impact in a number of large scale clinical trials. These trials include the DASH (1,2,3,4,5), DASH-Sodium (6,7) studies, the behavioral intervention trials—PREMIER (8,9,10,11,12), the ENCORE study (13,14), the Weight Loss Maintenance (WLM) (15,16) study, Hypertension Improvement Project (17,18), a Sino-US weight loss study (19). Currently I am collaborating with other investigators on the CITY clinical trial (20) examining the impact of a cell phone intervention for weight loss, the ENLIGHTEN study examining the impact of the DASH dietary pattern and a combined intervention on neurocognition (21), and two clinical trials examining the impact of carbohydrate restriction on markers of prostate cancer. For all these trials, even though the primary interest of outcome condition may vary, the underlying intervention strategy is similar, i.e., through lifestyle modification. Below summarizes three main areas of my research.
Diet and hypertension
Hypertension is a major risk factor for coronary heart disease, stroke, and premature death, and affects approximately one third of adults in the United States. Approximately another one third of the U.S. adults have prehypertension, which is also associated with a graded, increased risk of cardiovascular disease and progression to hypertension. Even though enormous advancement has been made in identifying evidence-based lifestyle strategies for hypertension prevention and management, little progress is made in implementing these proven strategies. My research in this area lies mainly in the development of dietary strategies for the prevention and management of hypertension (22), such as the DASH dietary pattern which has been included in the JNC guidelines (JNC). In collaboration with Dr. Laura Svetkey, we have collectively conducted many lifestyle intervention trials (DASH, DASH-Sodium, PREMIER, HIP) and observed the power of nutrition and lifestyle intervention on blood pressure and many other health indicators. Unfortunately, evidence-based recommendations do not always translate into practice. For example, the recommendation of following the DASH dietary pattern has fared poorly in the US. Adherence of both the clinicians in making the recommendation and the public in adoption has been less than satisfactory. Undoubtedly, implementing dietary and lifestyle modifications is challenging, and effective strategies for sustainable implementation are urgently needed. Thus, my research continues to seek science-based practical information for health care providers to provide effective lifestyle intervention and for the public to follow for blood pressure care (23). In a small randomized controlled feeding study, I also initiated the research direction of identifying the mechanism behind the blood pressure lowering effect of the DASH dietary pattern (DASH-Mechanism study) (24).
Diet and weight control
The obesity epidemic remains a serious health issue in US and it is closely related to development of several chronic diseases. Several trials indicate that weight loss can be achieved, and to some extent sustained. Dietary intake and lifestyle contribute substantially to weight control, however, management of these behaviors require more than knowledge, strategy such as tracking or self-monitoring has been proven to be effective. I have collaborated with various investigators in identifying effective platforms in delivering these proven strategies for weight loss and maintenance. In view of the growing popularity in cell phone usage, in collaboration with Dr. Gary Bennett, we completed a weight loss study in Beijing China with 120 overweight participants using text messaging as the platform in delivering the intervention (19). CITY clinical trial (20,25) is another example where we are developing cell phone apps in delivering effective intervention strategies for weight loss and its maintenance among young adults. It is in the final data collection phase and the main result is expected to be ready in the summer of 2014.
Diet and prostate cancer
Prostate cancer (PCa) is the second most common cancer in men, with nearly a million new cases diagnosed worldwide per year, and approximately a six-fold higher incidence in Western than in non-Western countries. Diet, lifestyle, environmental, and genetic factors are hypothesized to play a role in these differences. Since insulin is a growth factor for PCa growth, it has been hypothesized that reducing carbohydrates and thus lowering serum insulin may slow PCa growth. Indeed, in animal models, either a no-carbohydrate ketogenic diet (NCKD) or a low-carbohydrate diet (20% kcal as carbohydrate) has favorable effects on slowing prostate tumor growth. In human studies, one study found that high intake of refined carbohydrates was associated with increased risk of PCa. In addition to the amount of carbohydrate, type of carbohydrate may impact on PCa. A high dietary glycemic index (GI) was positively associated with incidence of PCa in case-control studies that was either population-based, among 2556 men or with aggressive PCa among 982 men. Furthermore, increasing intake of lower GI foods including leafy and carotenoid vegetables were inversely associated with risk of aggressive PCa. However, other studies have not found an association between carbohydrate intake, GI or GL with PCa risk. Despite the potential for reducing either total or simple carbohydrates in benefiting PCa control, evidence is lacking from controlled randomized trials. Thus, I am collaborating with Dr. Stephen Freedland on two on-going randomized trials examining the impact of a low-carbohydrate diet (20% kcal) on either the PSA doubling time among PCa patients post radical prostatectomy or on glycemic response among patients initiating hormone therapy (CASP1&2). Both trials are in the recruiting phase and plan to complete data collection in 2016.