This review utilizes current national dietary guidelines and published databases to evaluate the impacts of reasonable shifts in the amount and type of protein intake in the United States on the intersection of human and environmental health. The established scientific basis and recommendations for protein intake as described in the US Dietary Reference Intakes are reviewed. Data on food availability from both the US Department of Agriculture and the Food and Agriculture Organization of the United Nations and data on consumption from the National Health and Nutrition Examination Survey are used to examine estimates of current US protein consumption. Greenhouse gas (carbon dioxide equivalents, CO 2 eq) and blue and green water impacts of US protein consumption resulting from US agricultural practices were obtained from previously published meta-analyses. A 25% decrease in protein intake paired with a 25% shift from animal food to plant food protein intake—from an 85:15 ratio to a 60:40 ratio—would best align protein intake with national dietary recommendations while simultaneously resulting in 40% fewer CO 2 eq emissions and 10% less consumptive water use. The modeling of this strategy suggests a savings of 129 billion kilograms of CO 2 eq and 3.1 trillion gallons of water relative to current consumption.

Numerous studies have attempted to identify successful dietary strategies for weight loss, and many have focused on Low-Fat vs. Low-Carbohydrate comparisons. Despite relatively small between-group differences in weight loss found in most previous studies, researchers have consistently observed relatively large between-subject differences in weight loss within any given diet group (e.g., ~25 kg weight loss to ~5 kg weight gain). The primary objective of this study was to identify predisposing individual factors at baseline that help explain differential weight loss achieved by individuals assigned to the same diet, particularly a pre-determined multi-locus genotype pattern and insulin resistance status. Secondary objectives included discovery strategies for further identifying potential genetic risk scores. Exploratory objectives included investigation of an extensive set of physiological, psychosocial, dietary, and behavioral variables as moderating and/or mediating variables and/or secondary outcomes. The target population was generally healthy, free-living adults with BMI 28-40 kg/m2 (n=600). The intervention consisted of a 12-month protocol of 22 one-hour evening instructional sessions led by registered dietitians, with ~15-20 participants/class. Key objectives of dietary instruction included focusing on maximizing the dietary quality of both Low-Fat and Low-Carbohydrate diets (i.e., Healthy Low-Fat vs. Healthy Low-Carbohydrate), and maximally differentiating the two diets from one another. Rather than seeking to determine if one dietary approach was better than the other for the general population, this study sought to examine whether greater overall weight loss success could be achieved by matching different people to different diets. Here we present the design and methods of the study.

OBJECTIVE To test for differential weight loss response to Low-Fat (LF) vs. Low-Carbohydrate (LC) diets by insulin resistance status with emphasis on overall quality of both diets. METHODS Sixty-one adults, BMI 28-40 kg/m2, were randomized in a 2X2 design to LF or LC by insulin resistance status in this pilot study. Primary outcome was 6-month weight change. Participants were characterized as more insulin resistant (IR) or more insulin sensitive (IS) by median split of baseline insulin-area-under-the-curve from an oral glucose tolerance test. Intervention consisted of 14 one-hour class-based educational sessions. RESULTS Baseline % carb:% fat:% protein was 44:38:18. At 6m the LF group reported 57:21:22 and the LC group reported 22:53:25 (IR and IS combined). Six-month weight loss (kg) was 7.4 ± 6.0 (LF-IR), 10.4 ± 7.8 (LF-IS), 9.6 ± 6.6 (LC-IR), and 8.6 ± 5.6 (LC-IS). No significant main effects were detected for weight loss by diet group or IR status; no significant diet X IR interaction. Significant differences in several secondary outcomes were observed. CONCLUSION Substantial weight loss was achieved overall, but a significant diet X IR status interaction was not observed. Opportunity to detect differential response may have been limited by the focus on high diet quality for both diet groups and sample size.

Background/objectives Biological sex factors and sociocultural gender norms affect the physiology and behavior of weight loss. However, most diet intervention studies do not report outcomes by sex, thereby impeding reproducibility. The objectives of this study were to compare 12-month changes in body weight and composition in groups defined by diet and sex, and adherence to a healthy low carbohydrate (HLC) vs. healthy low fat (HLF) diet. Participants/methods This was a secondary analysis of the DIETFITS trial, in which 609 overweight/obese nondiabetic participants (age, 18–50 years) were randomized to a 12-month HLC (n = 304) or HLF (n = 305) diet. Our first aim concerned comparisons in 12-month changes in weight, fat mass, and lean mass by group with appropriate adjustment for potential confounders. The second aim was to assess whether or not adherence differed by diet-sex group (HLC women n = 179, HLC men n = 125, HLF women n = 167, HLF men n = 138). Results 12-month changes in weight (p < 0.001) were different by group. HLC produced significantly greater weight loss, as well as greater loss of both fat mass and lean mass, than HLF among men [−2.98 kg (−4.47, −1.50); P < 0.001], but not among women. Men were more adherent to HLC than women (p = 0.02). Weight loss estimates within group remained similar after adjusting for adherence, suggesting adherence was not a mediator. Conclusions By reporting outcomes by sex significant weight loss differences were identified between HLC and HLF, which were not recognized in the original primary analysis. These findings highlight the need to consider sex in the design, analysis, and reporting of diet trials.

Both vegetable and fruit consumption contribute to wellness and disease prevention. Most dietary health messages promote both together and position the word "fruits" before "vegetables." We examined the word order of the commonly used phrase "fruits and vegetables" through linguistics, psychology, botany, nutrition, health outcomes, and current US intake to determine if the common word order best presents these two foods in health messaging. By comparing the 10 most commonly consumed vegetables versus fruits, we found that vegetables scored higher on the Aggregate Nutrient Density Index and contained fewer calories and more fiber than fruits. Among the "nutrients of public concern" listed in the 2015 Dietary Guidelines for Americans, we determined that vegetables are better sources of these nutrients than fruits, although fruits scored higher in antioxidant content. In observational cohort studies, vegetable and fruit consumption was found to be associated with decreased mortality. Finally, daily intakes of both vegetables and fruits are lower than recommended, but the discrepancy is larger for vegetables-especially among children-suggesting a greater imperative to promote vegetables. For these reasons, future health messages promoting both together should intentionally put "vegetables" first to promote intake and emphasize their importance regarding contribution to health.