The Science Behind the New Dietary Guidelines: What Changed and Why

The Dietary Guidelines for Americans, 2025–2030, are accompanied by a Scientific Foundation report and a set of supplementary scientific reviews published as appendices.^[1][2] Together, these documents comprise the evidentiary basis for the new guidelines. 

This article examines the scientific evidence underlying each major recommendation change, the advisory committee process that preceded publication, and the areas where the final guidelines diverged from the committee’s recommendations.

We distinguish between evidence from randomized controlled trials (RCTs), observational cohort studies, and systematic reviews, and note where the evidence base is strong, mixed, or limited. Where the final guidelines adopted or rejected advisory committee recommendations, the stated rationale is documented.

The Dietary Guidelines Advisory Committee Process

The development of each edition of the Dietary Guidelines follows a structured process. USDA and HHS appoint a Dietary Guidelines Advisory Committee (DGAC), composed of external scientific experts, to review the current body of nutrition evidence and produce a scientific report with recommendations.

For the 2025–2030 cycle, a 20-member DGAC was appointed during the Biden Administration. The committee submitted its Scientific Report of the 2025 Dietary Guidelines Advisory Committee (referred to as the DGAC Report) following a multi-year review process.

The Trump Administration, upon taking office, conducted an independent supplemental evidence review. The stated rationale was that the DGAC Report had framed its analysis through a health equity lens, which the administration described as an interpretive filter that could shape scientific conclusions rather than allowing science to inform policy independently. The term “health equity” appeared more than 170 times in the DGAC Report.^[2]

To conduct the supplemental analysis, nutrition scientists and subject matter experts were selected through a federal contracting process. Standardized protocols were established governing study inclusion criteria, quality assessment, and evidence grading. All reviews underwent external peer review coordinated by the NIH Office of Nutrition Research. The resulting document—the Scientific Foundation for the Dietary Guidelines for Americans, 2025–2030—was finalized as the evidentiary basis for the published guidelines.^[2]

What the Advisory Committee Recommended: Accepted and Rejected

The Scientific Foundation report includes a detailed accounting of which DGAC recommendations were implemented, partially implemented, or rejected.

Protein: From 0.8 g/kg to 1.2–1.6 g/kg

The single largest quantitative change in the 2025–2030 guidelines is the protein recommendation. The guidelines now recommend 1.2–1.6 grams of protein per kilogram of body weight per day, compared to the previous Recommended Dietary Allowance (RDA) of 0.8 g/kg.

The Scientific Basis

The Scientific Foundation report’s Appendix 4.9 (High-Quality, Nutrient-Dense Protein Foods) conducted a rapid systematic review of RCTs evaluating the effects of higher protein diets on weight management and body composition. The review identified 18 prior systematic reviews and meta-analyses on the topic. Of these, 16 of 18 (89%) reported improved weight management outcomes—including greater weight loss, greater fat loss, less weight regain, or greater lean mass preservation—following diets providing protein above 0.8 g/kg body weight per day.^[3]

The report established the following criteria for what constitutes higher dietary protein: intake of 1.2 g/kg body weight or higher, or 20–35% of daily energy from protein. For comparison, the existing DGA dietary patterns contain approximately 15–18% of energy as protein.

A key finding of the supplementary review was that the previous RDA of 0.8 g/kg was established to prevent protein deficiency based on nitrogen-balance data. It was not designed as a target for optimal health, weight management, or chronic disease prevention.^[3][8] The report frames the new range of 1.2–1.6 g/kg as a health-promotion target rather than a minimum adequacy threshold.

The review also addressed protein quality and source. Animal-source protein foods (ASPFs) contain 3 to 4 times more essential amino acids (EAAs) per serving than beans, peas, and lentils, and provide 20–27 grams of protein per serving compared to 6–8 grams from plant sources.^[3] The report found that replacing ASPFs with beans, peas, and lentils would reduce protein and EAA density and reduce several under-consumed micronutrients including heme iron, zinc, vitamin B12, choline, and selenium.^[3]

The report modeled a “Higher-Protein Dietary Pattern” at 2,000 calories providing approximately 122 grams of protein per day (24% of energy from protein). This pattern met recommended intake levels for nearly all nutrients evaluated, with the exceptions of vitamin D, vitamin E, and choline in males—the same shortfalls found in all three existing USDA dietary patterns.

Evidence Strength

The protein evidence base includes multiple RCTs of varying duration and design. The report’s rapid systematic review applied inclusion criteria requiring studies of at least 12 weeks’ duration with controlled dietary interventions. The consistency of findings across 16 of 18 meta-analyses provides a relatively strong evidence base for the weight management benefits of protein intake above 0.8 g/kg. However, the report acknowledged that the evidence does not identify a single optimal protein intake; instead, a range is appropriate to accommodate individual variation in energy needs, health status, and dietary preferences. The safe upper range for dietary protein is supported by published studies at levels in excess of 2.5 g/kg body weight per day.^[3]

Ultra-Processed Foods: The First-Ever Federal Warning

The 2025–2030 Dietary Guidelines include the first explicit federal recommendation to avoid highly processed foods. No prior edition of the Dietary Guidelines addressed food processing as a dietary concern.

The Evidence Base

The Scientific Foundation report’s Appendix 4.1 conducted an umbrella review of epidemiological meta-analyses examining the association between ultra-processed food (UPF) consumption and health outcomes. The review identified broad and consistent associations across multiple chronic disease endpoints, including type 2 diabetes, cardiovascular disease, liver disease, dementia, depression, and all-cause mortality. Several of these outcomes were graded as high-certainty evidence within the umbrella review framework.^[3][13]

The prior DGAC had also commissioned a systematic review on UPF and health outcomes, but that review was limited to growth, body composition, and obesity risk, and only included cohorts with more than 1,000 participants. The DGAC review concluded that associations were present but limited in strength. The supplementary review conducted for the Scientific Foundation extended substantially beyond the DGAC’s scope, incorporating nearly two additional years of evidence beyond the DGAC’s literature cutoff of January 2024. The supplementary review included previously published meta-analyses of prospective cohort studies and randomized controlled trials, required a well-defined classification for processed food consumption, assessed clinical chronic disease endpoints, and required that at least one study from the United States was included in each meta-analysis.

A 2024 umbrella review of meta-analyses (Lane et al., 2024) provided additional context, documenting consistent associations between UPF consumption and adverse health outcomes across multiple domains.^[5] An NIH-funded RCT (Hall et al., 2019) demonstrated that participants consuming ultra-processed diets ate approximately 500 more calories per day and gained weight compared to those consuming unprocessed diets matched for macronutrients.^[6]

Data from NHANES show that ultra-processed food consumption among U.S. youth increased from 61.4% of total calories in 1999 to 67.0% in 2018.^[7] Among adults, UPF consumption rose from 53.5% in 2001–2002 to 57% in 2017–2018.^[3]

Limitations

The Scientific Foundation report identifies several important limitations in the UPF evidence base. First, a consensus definition for highly processed foods does not yet exist. A joint USDA-FDA effort to establish a uniform definition is underway.^[3] The NOVA classification system, which is the most widely used in research, does not designate refined cooking ingredients (such as refined starches, added sugars, or extracted oils) as ultra-processed, and can classify some nutrient-dense foods as ultra-processed.^[11]

Second, existing RCTs testing the effects of processed foods are of relatively short duration, include small to moderate sample sizes, and are limited to effects on metabolic markers, body weight, and adiposity.^[2] The majority of evidence linking UPF to adverse health outcomes is derived from observational, non-randomized studies, which are subject to confounding from factors such as healthy adherer bias, reverse causation, and other factors.^[2] No study to date has demonstrated health benefits associated with processed food consumption.^[3]

Added Sugar: Stricter Limits for Children and Adults

The 2025–2030 guidelines adopt stricter added sugar limits than any prior edition. For adults, no more than 10 grams of added sugars per meal is recommended. For children ages 5–18, no amount of added sugars is recommended. Added sugars should be avoided entirely during infancy and early childhood.^[1]

The previous 2020–2025 guidelines set the limit at less than 10% of calories from added sugars beginning at age 2. The 2025–2030 guidelines substantially tighten this standard, particularly for pediatric populations.

The Scientific Foundation report frames the added sugar limits within the broader context of the recommendation to avoid highly processed foods, noting that highly processed foods are significant sources of added sugars, refined grains, and extracted oils.^[2] The World Health Organization (WHO) Guideline on Sugars Intake for Adults and Children recommends reducing free sugars to less than 10% of total energy intake, with a conditional recommendation to reduce further to below 5%.^[9] The new U.S. guidelines for children effectively go beyond the WHO recommendation.

CDC/NHANES data document that added sugars remain a significant component of the American diet, particularly among children and adolescents. The high prevalence of childhood obesity and prediabetes—the guidelines cite that nearly one in three adolescents ages 12–17 has prediabetes^[1]—provided the public health rationale for the stricter limits.

Full-Fat Dairy: Reversing Decades of Low-Fat Guidance

The 2025–2030 guidelines explicitly recommend full-fat dairy with no added sugars, reversing decades of federal guidance emphasizing low-fat or fat-free dairy products.^[1] 

The Stated Rationale

The Scientific Foundation report’s chapter on fats and oils presents a detailed examination of the dairy fat evidence. The key finding: there is a “remarkable lack of evidence from RCTs and observational studies demonstrating adverse clinical consequences of whole-fat dairy in adults or children.”^[2][14]

The report further argues that the historical emphasis on reducing saturated fat in dairy inadvertently encouraged the consumption of highly processed dairy products. The report uses yogurt as a case study: whole-fat yogurt made from one ingredient (whole milk) provides roughly 18 grams of protein per serving but is ineligible for health claims due to saturated fat content. Meanwhile, low-fat and fat-free yogurts—which qualify for “Low Saturated Fat” health claims—contain 8 or more ingredients, 30–70% less protein, and up to 16–26 grams of added sugar, along with modified corn starch, artificial sweeteners, emulsifiers, and chemical additives.^[2]

The report cites observational evidence suggesting that consumption of ultra-processed dairy products was associated with higher all-cause mortality in a nationally representative sample of U.S. adults. Cumulative exposures to emulsifiers commonly added to low- or nonfat dairy foods were associated with increased risk of incident type 2 diabetes, cancer, and cardiovascular disease in a large French cohort.^[2] 

Saturated Fat: The 10% Limit Maintained, Context Changed

The 2025–2030 guidelines maintain the recommendation that saturated fat should not exceed 10% of total daily calories.^[1] However, the accompanying Scientific Foundation report provides substantial new context that reframes how this recommendation should be interpreted.

The report states: “A half century of research has not confirmed that lowering saturated fat below 10% of energy—or substituting it with linoleic acid–rich oils—reduces coronary heart disease or mortality risk.” Applying the GRADE certainty framework, which evaluates confidence in evidence based on study design and limitations such as bias, inconsistency, and imprecision ,the report rates the evidence as moderate certainty that reducing saturated fat has no effect on mortality and very low certainty for Coronary Heart Disease (CHD) events due to inconsistency and imprecision.^[2]

The report examines the historical RCTs testing the diet-heart hypothesis—the theory that replacing saturated fat with polyunsaturated fat (specifically linoleic acid–rich oils) reduces cardiovascular disease. It identifies significant confounders in several foundational trials and concludes that the RCT evidence does not provide causal support for reducing saturated fat below 10% of energy or replacing it with linoleic acid–rich oils to prevent CHD or death.

The practical effect of this framing is that the 10% limit is maintained as a threshold but not as a target for further reduction. Foods naturally containing saturated fat—such as full-fat dairy, eggs, and meat—are endorsed as part of healthy dietary patterns when consumed in reasonable amounts within minimally processed contexts. While the current evidence does not support reducing saturated fat below 10% of energy, the report recognizes that this remains an active area of scientific inquiry. Future research — particularly well-designed randomized controlled trials — will be critical to refining these recommendations as the evidence base continues to develop.

Cooking Oils and Linoleic Acid: A New Area of Concern

The 2025–2030 guidelines recommend prioritizing olive oil when cooking with or adding fats to meals.^[1] The Scientific Foundation report devotes substantial attention to the health implications of cooking with linoleic acid–rich oils (such as soybean, corn, and sunflower oils), a topic not addressed in prior editions of the guidelines.

It documents that linoleic acid intake has increased substantially over the past century due to industrial processing and dietary guidance favoring “unsaturated” or “polyunsaturated” fats. Linoleic acid now contributes an estimated 7.6% of food energy—several times higher than pre-industrial levels. Published evidence shows that cooking or frying with linoleic acid–rich oils produces larger amounts of lipid hydroperoxides and aldehydes than oleic acid or saturated fat–containing oils. These oxidation products are absorbed into plasma lipoproteins and tissues and have been implicated in the etiology of multiple chronic diseases.^[2]

The report identifies this as an area where the evidence is sufficient to raise concern but insufficient for definitive conclusions. It lists several high-priority RCTs needed to resolve outstanding questions, including trials comparing the health effects of cooking with high-oleic versus high-linoleic oils and trials testing whether lowering linoleic acid intake from current U.S. levels improves cardiometabolic outcomes.

Refined Carbohydrates: The Evidence for Reduction

The guidelines recommend significantly reducing consumption of highly processed, refined carbohydrates, including white bread, ready-to-eat or packaged breakfast options, flour tortillas, and crackers. Whole grains serving goals are set at 2–4 servings per day, a substantial reduction from the 1992 pyramid’s 6–11 servings of grains.^[1]

The Scientific Foundation report’s appendix on refined carbohydrates concludes that refined carbohydrates are uniquely capable of driving hyperinsulinemia and insulin resistance through both rapid glycemic effects and behavioral mechanisms of low satiety and high reward. Cohort studies demonstrate increased risk of type 2 diabetes at high intakes, while clinical trials show improvements in insulin sensitivity and glycemic control when refined carbohydrates are reduced or replaced with low-glycemic-index alternatives.^[3]

The report states that historical dietary guidelines that emphasized total carbohydrate intake without distinguishing between refined and unrefined sources contributed to overconsumption of refined carbohydrates, with lasting public health consequences. The new guidelines’ approach—specifying whole grains only and explicitly naming refined carbohydrate products to reduce—represents a departure from prior editions that set grain targets without specifying quality.

Alcohol

The Scientific Foundation report notes that guidance on alcoholic beverages and health in this edition was informed by a study conducted by the National Academies of Sciences, Engineering, and Medicine (NASEM).^[10] The report directs readers to the NASEM report for detailed evidence on this topic.

Future Research Priorities

While there is an evidence base to support the report’s recommendations, more RCTs could help resolve outstanding questions, including:

• Whether cooking with peroxidation-resistant oils (such as high-oleic soybean or olive oil) improves health outcomes compared to linoleic acid–rich oils (such as conventional soybean and corn oil). 
• Whether replacing highly processed foods with minimally processed diets reduces levels of food packaging contaminants — such as microplastics and phthalates — that have been shown to accumulate in human blood, tissues, and brains. 
• The long-term clinical effects of specific food additives, including emulsifiers, artificial sweeteners, and petroleum-based dyes. 
• Whether replacing artificial sweeteners with other alternatives has beneficial, harmful, or neutral metabolic and health effects. 
• Which type of dairy — whole-fat, low-fat, or fat-free — best supports metabolic health, particularly in children. 
• The effects of reducing highly processed foods on clinical endpoints including cardiometabolic and neurological diseases. 

The report frames this edition as “a first, deliberate step toward modernizing national nutrition guidance” and states that its long-term success will depend on researchers, funders, and policymakers collaborating to build the next generation of nutrition evidence. 

References

^[1] U.S. Department of Agriculture; U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2025–2030. Washington (DC): U.S. Department of Agriculture; 2026 Jan. Available from: https://cdn.realfood.gov/DGA.pdf

^[2] U.S. Department of Agriculture; U.S. Department of Health and Human Services. Scientific Foundation for the Dietary Guidelines for Americans, 2025–2030. Washington (DC): U.S. Department of Agriculture; 2025. Available from: https://cdn.realfood.gov/Scientific%20Report.pdf

^[3] U.S. Department of Agriculture; U.S. Department of Health and Human Services. Scientific Foundation for the Dietary Guidelines for Americans, 2025–2030: Appendices. Washington (DC): U.S. Department of Agriculture; 2026. Available from: https://cdn.realfood.gov/Scientific%20Report%20Appendices_FINAL_1.28.26.pdf

^[4] DietaryGuidelines.gov. Scientific Report of the 2025 Dietary Guidelines Advisory Committee. Washington (DC): U.S. Department of Health and Human Services; U.S. Department of Agriculture; 2025. Available from: https://www.dietaryguidelines.gov/2025-advisory-committee-report

^[5] Lane MM, Gamage E, Du S, et al. Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses. BMJ. 2024; 384:e077310. doi:10.1136/bmj-2023-077310.

^[6] Hall KD, Ayuketah A, Brychta R, et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metab. 2019;30(1):67-77.e3. doi:10.1016/j.cmet.2019.05.008.

^[7] Wang L, Martínez Steele E, Du M, et al. Trends in consumption of ultraprocessed foods among US youths aged 2-19 years, 1999-2018. JAMA. 2021;326(6):519-530. doi:10.1001/jama.2021.10238.

^[8] Wolfe RR, Cifelli AM, Kostas G, Kim IY. Optimizing protein intake in adults: interpretation and application of the Recommended Dietary Allowance compared with the acceptable macronutrient distribution range. Adv Nutr. 2017;8(2):266-275. doi:10.3945/an.116.013821

^[9] World Health Organization. Guideline: sugars intake for adults and children. Geneva: World Health Organization; 2015. Available from: https://www.who.int/publications/i/item/9789241549028

^[10] National Academies of Sciences, Engineering, and Medicine. Review of evidence on alcohol and health. Washington (DC): National Academies Press; 2025. Available from: https://nap.nationalacademies.org/catalog/28582/review-of-evidence-on-alcohol-and-health

^[11] Monteiro CA, Cannon G, Levy RB, et al. The UN Decade of Nutrition, the NOVA food classification and the trouble with ultra-processing. Public Health Nutr. 2018;21(1):5-17. doi:10.1017/S1368980017000234.

^[12] Srour B, Fezeu LK, Kesse-Guyot E, et al. Ultra-processed food intake and risk of cardiovascular disease: prospective cohort study (NutriNet-Santé). BMJ. 2019;365:l1451. doi:10.1136/bmj.l1451.

^[13] de Souza RJ, Mente A, Maroleanu A, et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ. 2015;351:h3978. doi:10.1136/bmj.h3978.

^[14] Mozaffarian D. Dairy foods, dairy fat, diabetes, and death: what can be learned from 3 large new investigations? Am J Clin Nutr. 2019;110(2):266-268. doi:10.1093/ajcn/nqz120.