Nutrisize Health Handbook, undergraduate edition
Eleven real studies and guidelines, each with a question to work through. Learn to read hazard ratios, confidence intervals, trials and guidelines on actual numbers from WHO, the CDC, the FDA, the NIH and leading journals.
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A cohort study follows people and compares groups. It can show that two things go together, not why. People who walk more also differ in health, income and habits.
A ratio compares a group with a reference group. A hazard ratio of 0.53 means the rate of the outcome was 47% lower than in the reference group, over the follow-up period. A ratio of 1.00 means no difference.
The interval shows the range of values the data are compatible with. For a ratio, an interval that includes 1.00 does not rule out no effect. For a difference, an interval that includes 0 does the same.
In a randomised trial a chance process assigns people to groups, which balances other differences on average. That is why trials speak more strongly about cause, and why they are usually shorter and smaller.
Frameworks such as GRADE rate how much confidence to place in a body of evidence (for example high, moderate, low, very low). A guideline can be a strong recommendation built on moderate-certainty evidence.
Self-reported activity and one-day food recalls are noisy. Wrist accelerometers and weighed food are better but rarer. Always ask what the number actually measured.
Worked cases
Each case gives the finding, then questions to try. The sources are listed so you can check every number.
A 2025 meta-analysis found that 7,000 steps a day was linked to a hazard ratio of 0.53 (95% CI 0.46 to 0.60) for all-cause mortality, compared with 2,000 steps. The benefit levelled off around 5,000 to 7,000 steps.
Source: Ding D, Nguyen B, Nau T, et al. Daily steps and health outcomes in adults. Lancet Public Health 2025;10:e668-e681. doi.org/10.1016/S2468-2667(25)00164-1
In the DIETFITS trial (609 adults, 12 months), weight change was -5.3 kg on a healthy low-fat diet and -6.0 kg on a healthy low-carbohydrate diet. The difference was 0.7 kg (95% CI -0.2 to 1.6). Neither a genotype pattern nor insulin secretion predicted who did better.
Source: Gardner CD et al. JAMA 2018;319(7):667-679 (DIETFITS). doi.org/10.1001/jama.2018.0245
In 139 adults with obesity, time-restricted eating (8:00 to 16:00) added to calorie restriction gave -8.0 kg versus -6.3 kg with calorie restriction alone at 12 months. The net difference was 1.8 kg (95% CI -4.0 to 0.4; P=0.11).
Source: Liu D et al. N Engl J Med 2022;386(16):1495-1504. doi.org/10.1056/NEJMoa2114833
Across 16 cohorts, muscle-strengthening activity was linked to 10 to 17% lower risk of death and chronic disease, with the largest gain at about 30 to 60 minutes a week. The curves for several outcomes were J-shaped.
Source: Momma H, Kawakami R, Honda T, Sawada SS. Muscle-strengthening activities are associated with lower risk and mortality in major non-communicable diseases. Br J Sports Med 2022;56(13):755-763. doi.org/10.1136/bjsports-2021-105061
In 2021 to 2023, ultra-processed foods supplied 55.0% of calories for Americans aged 1 and over, 61.9% for ages 1 to 18 and 53.0% for adults. The data come from one 24-hour recall per person, classified with the NOVA system.
Source: Williams AM, Couch CA, Emmerich SD, Ogburn DF. Ultra-processed Food Consumption in Youth and Adults: United States, August 2021-August 2023. NCHS Data Brief No. 536, 2025. https://cdc.gov/nchs/products/databriefs/db536.htm
A WHO-commissioned set of reviews pooled 185 prospective studies and 58 trials. Highest versus lowest fibre intake was linked to 15 to 30% lower all-cause and cardiovascular mortality and lower risk of several diseases, with the greatest reduction at 25 to 29 g a day. Certainty was moderate for fibre.
Source: Reynolds A et al. Carbohydrate quality and human health. Lancet 2019;393(10170):434-445. doi.org/10.1016/S0140-6736(18)31809-9
Eighty adults aged 21 to 40 with overweight, who usually slept under 6.5 hours, were asked to extend sleep by about 1.2 hours a night for two weeks. They ate about 270 fewer calories a day (95% CI -393 to -147).
Source: Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. JAMA Intern Med 2022;182:365-374. doi.org/10.1001/jamainternmed.2021.8098
In the NIH Diabetes Prevention Program (3,234 participants), a lifestyle programme aiming for 7% weight loss and 150 minutes of activity a week lowered diabetes risk by 58% versus placebo, and metformin by 31%. When Medicare offered the programme to 9,015 beneficiaries, average weight loss was 4.9%.
Source: Diabetes Prevention Program (DPP), NIDDK, reviewed August 2021. https://www.niddk.nih.gov/about-niddk/research-areas/diabetes/diabetes-prevention-program-dpp; Medicare Diabetes Prevention Program Expanded Model: Findings at a Glance (April 2018 to March 2024), CMS Innovation Center, 2025. https://www.cms.gov/priorities/innovation/data-and-reports/2025/mdpp-finalevalrpt-fg
WHO's 2020 guidelines for adults recommend 150 to 300 minutes of moderate (or 75 to 150 minutes of vigorous) activity a week, plus muscle strengthening on 2 or more days. The strengthening advice is a strong recommendation based on moderate-certainty evidence, and benefits appear below the targets.
Source: Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med 2020;54:1451-1462. doi.org/10.1136/bjsports-2020-102955
The FDA's Daily Value for added sugars is 50 g a day on a 2,000-calorie diet. A label showing 5% Daily Value or less is low; 20% or more is high. Sodium's Daily Value is 2,300 mg and fibre's is 28 g.
Source: Added Sugars on the Nutrition Facts Label, FDA (content current March 2026). https://www.fda.gov/food/nutrition-facts-label/added-sugars-nutrition-facts-label; Daily Value on the Nutrition and Supplement Facts Labels, FDA. https://www.fda.gov/food/nutrition-facts-label/daily-value-nutrition-and-supplement-facts-labels
WHO recommends under 2,000 mg of sodium a day. The US Daily Value is 2,300 mg, and the National Academies set an adequate intake of 1,500 mg with a risk-reduction intake of 2,300 mg. The average US intake is about 3,400 mg and the global mean 4,278 mg.
Source: Sodium reduction fact sheet, WHO, 11 May 2026. https://www.who.int/news-room/fact-sheets/detail/sodium-reduction; Dietary Reference Intakes for Sodium and Potassium, National Academies of Sciences, Engineering, and Medicine, 2019. https://nationalacademies.org/news/2019/03/sodium-and-potassium-dietary-reference-intake-values-updated-in-new-report; Sodium Reduction in the Food Supply, FDA, 2024. https://www.fda.gov/food/nutrition-food-labeling-and-critical-foods/sodium-reduction-food-supply
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App StoreGoogle PlayThis handbook is a compilation, paraphrased from the cited public sources, with each figure traceable to its source; it is not a peer-reviewed publication. It provides health and wellness information for educational purposes and is not medical advice. Consult your clinician before changing your diet or exercise. Published by Nutrisize Health, a product of EqualInformation, LLC, Sunnyvale, CA, USA. October 2026.
Other editions
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OpenHandbook for researchers and clinicians
OpenHandbook for K-12 teachers: movement, food and evidence literacy
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