Expert Discusses Which Diets Are Best, Based on the Evidence




"Evidence from studies can help clinicians and their patients develop a successful dietary management plan and achieve optimal health," said internist Michelle Hauser, MD, clinical associate professor at Stanford (Calif.) University. She also discussed evidence-based techniques to support patients in maintaining dietary modifications.


Predominantly plant‐based diets
Popular predominantly plant‐based diets include a Mediterranean diet, healthy vegetarian diet, predominantly whole-food plant‐based (WFPB) diet, and a dietary approach to stop hypertension (DASH).


The DASH diet was originally designed to help patients manage their blood pressure, but evidence suggests that it also can help adults with obesity lose weight. In contrast to the DASH diet, the Mediterranean diet is not low-fat and not very restrictive. Yet the evidence suggests that the Mediterranean diet is not only helpful for losing weight but also can reduce the risk of various chronic diseases, including obesity, type 2 diabetes, cardiovascular disease (CVD), and cancer, Dr. Hauser said. In addition, data suggest that the Mediterranean diet may reduce the risk of all-cause mortality and lower the levels of cholesterol.


"I like to highlight all these protective effects to my patients, because even if their goal is to lose weight, knowing that hard work pays off in additional ways can keep them motivated," Dr. Hauser stated.


A healthy vegetarian diet and a WFPB diet are similar, and both are helpful in weight loss and management of total cholesterol and LDL‐C levels. Furthermore, healthy vegetarian and WFPB diets may reduce the risk of type 2 diabetes, CVD, and some cancers. Cohort study data suggest that progressively more vegetarian diets are associated with lower BMIs.


"My interpretation of these data is that predominantly plant-based diets rich in whole foods are healthful and can be done in a way that is sustainable for most," said Dr. Hauser. However, this generally requires a lot of support at the outset to address gaps in knowledge, skills, and other potential barriers.


For example, she referred one obese patient at risk of diabetes and cardiovascular disease to a registered dietitian to develop a dietary plan. The patient also attended a behavioral medicine weight management program to learn strategies such as using smaller plates, and his family attended a healthy cooking class together to improve meal planning and cooking skills.
Time‐restricted feeding
There are numerous variations of time-restricted feeding, commonly referred to as intermittent fasting, but the principles are similar – limiting food intake to a specific window of time each day or week.


Although some studies have shown that time-restricted feeding may help patients reduce adiposity and improve lipid markers, most studies comparing time-restricted feeding to a calorie-restricted diet have shown little to no difference in weight-related outcomes, Dr. Hauser said.


These data suggest that time-restricted feeding may help patients with weight loss only if time restriction helps them reduce calorie intake. She also warned that time-restrictive feeding might cause late-night cravings and might not be helpful in individuals prone to food cravings.


Low‐carbohydrate and ketogenic diets
Losing muscle mass can prevent some people from dieting, but evidence suggests that a high-fat, very low-carbohydrate diet – also called a ketogenic diet – may help patients reduce weight and fat mass while preserving fat‐free mass, Dr. Hauser said.


The evidence regarding the usefulness of a low-carbohydrate (non-keto) diet is less clear because most studies compared it to a low-fat diet, and these two diets might lead to a similar extent of weight loss.


Rating the level of scientific evidence behind different diet options
Nutrition studies do no provide the same level of evidence as drug studies, said Dr. Hauser, because it is easier to conduct a randomized controlled trial of a drug versus placebo. Diets have many more variables, and it also takes much longer to observe most outcomes of a dietary change.


n addition, clinical trials of dietary interventions are typically short and focus on disease markers such as serum lipids and hemoglobin A1c levels. To obtain reliable information on the usefulness of a diet, researchers need to collect detailed health and lifestyle information from hundreds of thousands of people over several decades, which is not always feasible. "This is why meta-analyses of pooled dietary study data are more likely to yield dependable findings," she noted.


Getting to know patients is essential to help them maintain diet modifications
When developing a diet plan for a patient, it is important to consider the sustainability of a dietary pattern. "The benefits of any healthy dietary change will only last as long as they can be maintained," said Dr. Hauser. "Counseling someone on choosing an appropriate long-term dietary pattern requires getting to know them – taste preferences, food traditions, barriers, facilitators, food access, and time and cost restrictions."


In an interview after the session, David Bittleman, MD, an internist at Veterans Affairs San Diego Health Care System, agreed that getting to know patients is essential for successfully advising them on diet.


"I always start developing a diet plan by trying to find out what [a patient's] diet is like and what their goals are. I need to know what they are already doing in order to make suggestions about what they can do to make their diet healthier," he said.


When asked about her approach to supporting patients in the long term, Dr. Hauser said that she recommends sequential, gradual changes. Dr. Hauser added that she suggests her patients prioritize implementing dietary changes that they are confident they can maintain.