Evidence and references.
Nutrition Handbook, 1st edition · Last updated: 12/08/2026
Every number in the Nutrition Handbook came from somewhere. This page is where nutrition research changes.
Guidelines get updated and better evidence sometimes changes what we recommend. Keeping the references online means they can change too, instead of ageing quietly inside a printed book.
If you find something here that is out of date or wrong, tell us. That is the process working.
The numbers
Every figure in the handbook is a starting point rather than a prescription. Here is where each one comes from.
Protein: 1.2 to 1.6 grams per kilogram per day
Two sources sit behind this range, and they are doing different jobs.
The lower end comes from the PROT-AGE position paper, which recommends 1.0 to 1.2 g/kg/day for older adults generally, rising to 1.2 to 1.5 g/kg/day for those who exercise or are managing illness. Since the handbook's range assumes regular resistance training, 1.2 is the floor rather than the middle.
The upper end comes from a meta-analysis of 49 studies and 1,863 participants, which found the benefit of additional protein for resistance-training gains stopped at roughly 1.62 g/kg/day. Eating more than that did not produce more muscle.
The same analysis found the effect of protein supplementation reduces with age, which is part of why we suggest midlife readers sit toward the upper end rather than the lower.
Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association.2013;14(8):542–559.
Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376–384.
Protein: 25 to 35 grams at each main meal
Adults over 60 need roughly 30 grams of protein in a meal to trigger muscle protein synthesis. Younger adults do not have this threshold and respond more or less in proportion to whatever they eat.
Worth being straight about the limits here. Whether spreading protein evenly across the day beats concentrating it is genuinely disputed. One study in younger adults found even distribution produced around 25 per cent more muscle protein synthesis, but two experimental studies in older adults did not replicate it, and a 2024 systematic review found no evidence that timing or frequency improved muscle mass in community-dwelling older adults.
This is why the handbook says total daily protein matters first and distribution second, and treats moving protein earlier as something to test rather than a promise.
There is a simpler argument for spreading it out, and it is the one we actually rely on. People who eat more protein at breakfast and lunch end up eating more protein across the whole day.
Impacts of protein quantity and distribution on body composition. Frontiers in Nutrition. 2024.
The effect of dose, frequency, and timing of protein supplementation on muscle mass in older adults: a systematic review and meta-analysis. Ageing Research Reviews. 2024.
Fibre: 25 grams a day for women, 30 for men
These are the Adequate Intake figures from the Australian Nutrient Reference Values.
There is a second, higher number worth knowing about. The Suggested Dietary Target, aimed at reducing chronic disease risk rather than simply adequate digestion, is 28 grams for women and 38 for men.
We used the lower figure because it is a more realistic starting point. Around 28 per cent of Australian adults currently meet it.
National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand.eatforhealth.gov.au
Alcohol: no more than 10 standard drinks a week and no more than 4 on any day
These are the current NHMRC guidelines, released in 2020.
Both limits apply together. Meeting one does not excuse the other.
One Australian standard drink contains 10 grams of pure alcohol. The type of drink makes no difference to that.
National Health and Medical Research Council. Australian Guidelines to Reduce Health Risks from Drinking Alcohol.2020. nhmrc.gov.au/health-advice/alcohol
Caffeine: around 400 mg a day
Food Standards Australia New Zealand concluded that habitual moderate caffeine intake is safe up to about 400 mg a day for adults.
Read the wording carefully, because it matters. There is no official health-based guidance value for caffeine. No Acceptable Daily Intake, no recommended limit. Four hundred milligrams is a figure commonly used as a ceiling. It is not a target and it is not a rule.
Food Standards Australia New Zealand. Caffeine.foodstandards.gov.au
Caffeine: stop at least six hours before bed
Researchers gave twelve healthy sleepers 400 mg of caffeine at zero, three and six hours before bedtime.
Even the dose taken six hours before bed reduced measured total sleep time by more than an hour.
The part worth knowing: participants largely did not notice. This is why the handbook says caffeine can affect your sleep even when you can still fall asleep.
Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. 2013;9(11):1195–1200.
Waist-to-height ratio below 0.5
A systematic review of 78 studies found the boundary value landed at 0.50 for both men and women, across fourteen countries and several ethnic groups. A separate meta-analysis covering more than 300,000 adults found waist-to-height ratio outperformed both waist circumference and BMI for predicting diabetes, hypertension and cardiovascular disease.
The simplest version of this measurement, and the one worth remembering: your waist should be less than half your height.
It is a screening guide, not a diagnosis.
Browning LM, Hsieh SD, Ashwell M. A systematic review of waist-to-height ratio as a screening tool for the prediction of cardiovascular disease and diabetes: 0.5 could be a suitable global boundary value. Nutrition Research Reviews.2010;23(2):247–269.
Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obesity Reviews. 2012;13(3):275–286.
Where we have taken a position
Some of the handbook says things the internet disagrees with. Here is the reasoning.
Your appetite is partly hunting for protein
The protein leverage hypothesis proposes that when protein makes up a small share of the diet, appetite keeps driving intake until protein needs are met.
There is human research supporting the effect. There is also good reason not to overstate it. Protein is not the only thing controlling appetite, and the response varies considerably between people.
The handbook treats it as one lever worth pulling rather than an appetite switch, and that is deliberate. It is a useful way to think about why protein-poor days leave you still hungry. It is not a mechanism you can rely on to do the work for you.
Older muscle responds less to protein
Researchers call this anabolic resistance. The stimulation of muscle protein synthesis from eating protein is blunted with age, so more protein is needed to reach the same response.
Note the hedging in the handbook, which is deliberate. Muscle can become less responsive, not does. At least one study found anabolic resistance did not occur in healthy older adults, and a recent systematic review found only three of eight studies showed a blunted response to resistance exercise in older versus younger people.
There is no universal age cut-off and no fixed doubling from 20 grams to 40 grams, whatever you may have read.
Aragon AA, Tipton KD, Schoenfeld BJ. Age-related muscle anabolic resistance: inevitable or preventable? Nutrition Reviews. 2023;81(4):441–454.
Lean mass on a scan is not the same thing as muscle
A DEXA scan does not weigh your muscle. It sorts your body into fat, bone and everything else, and calls that last category lean mass. Your muscle is in there, along with your blood, your organs, your water and your stored glycogen.
Some findings that make this concrete. Glycogen loading has been shown to increase measured lean mass by around 2 per cent. Creatine loading by around 1 per cent. Drinking a litre of water, or eating a standard meal, can raise lean body mass estimates by more than a kilogram within an hour.
Nothing about the person changed. The reading did.
This is why the handbook insists on the same preparation and, where possible, the same machine. It is also why a single scan tells you much less than two scans taken under matched conditions.
GLP-1 medications and lean mass
This is where the handbook says the scary headlines overstate the muscle story, so it is worth showing the working.
The trials do report substantial lean mass loss. In STEP-1, lean mass made up about 45 per cent of total weight lost. In SUSTAIN-8, about 43 per cent. In SURMOUNT-1, using tirzepatide, about 26 per cent. Across the wider literature the figure ranges from roughly 15 per cent to 60 per cent.
Those numbers get reported as muscle loss. They are not muscle loss.
Lean mass on a scan includes water, glycogen, blood and organ tissue alongside muscle. During rapid weight loss a meaningful share of what leaves is water and the glycogen stored with it. That is the section above, and it is the reason the same number reads very differently depending on whether you know what is being measured.
Two further findings sit alongside the headline figure. In both STEP-1 and SUSTAIN-8, lean mass as a proportion of total body mass went up, not down. And a twelve-month study using DXA found lean mass declined for the first seven months then stabilised, while grip strength improved by 4.5 kilograms and the prevalence of sarcopenic obesity fell from 49 per cent to 33 per cent.
None of which makes the concern imaginary. The handbook is explicit that for someone who already has low strength, low muscle mass, frailty or osteoporosis risk, protecting physical function belongs in the plan from the start. Protein and resistance training are the tools, and they matter more during medication-assisted weight loss rather than less.
Neeland IJ, et al. Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes, Obesity and Metabolism. 2024.
Impact of semaglutide on fat mass, lean mass and muscle function in patients with obesity (SEMALEAN). 2025.
The microbiome is real. The testing kits are not ready.
Researchers sent the same standardised, homogenised stool sample to seven different direct-to-consumer testing services.
The variation between companies was on the same scale as the variation between different people's samples. Which company you post to affects your result about as much as whose gut it came from.
There is also a conflict of interest worth naming. Many testing companies also sell the supplements and meal plans their reports recommend.
Servetas SL, Gierz KS, Hoffmann D, et al. Evaluating the analytical performance of direct-to-consumer gut microbiome testing services. Communications Biology. 2026.
Direct-to-consumer microbiome testing needs regulation. The Lancet Gastroenterology and Hepatology. 2024.
Autophagy does not switch on at a particular hour
Autophagy is real. The claim that it begins after a specific number of fasting hours is not established in humans, and most of the commonly quoted timings come from animal studies.
A 2025 study measured autophagic flux directly in people doing time-restricted eating and found no significant increase from baseline.
Bensalem J, et al. Intermittent time-restricted eating may increase autophagic flux in humans: an exploratory analysis. The Journal of Physiology. 2025.
Creatine gets a green light
Creatine monohydrate is among the better-supported supplements for strength and training performance when combined with resistance training. In older adults it has shown benefits for lean mass, strength, bone measures and functional ability, mostly when paired with training.
On cognition, the evidence is newer and the effects smaller. A meta-analysis of sixteen trials found improvements in memory, attention time and processing speed, but no significant effect on overall cognitive or executive function. Several of the studies in older adults are cross-sectional rather than controlled trials.
Kreider RB, Kalman DS, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition.2017;14:18.
Candow DG, et al. Creatine monohydrate supplementation for older adults and clinical populations. Journal of the International Society of Sports Nutrition. 2025.
Collagen is not a substitute for your main protein
Collagen contains virtually no tryptophan and very little leucine, which are the amino acids that trigger muscle building. It scores poorly on standard protein quality measures for exactly that reason.
What it does contain in quantity is glycine, proline and hydroxyproline, which are the building blocks of connective tissue. That is why a connective-tissue signal exists in the research while a muscle signal does not.
A 2026 systematic review found so much variation between protocols and outcomes that the authors declined to pool the results, and concluded the evidence does not support collagen for improving strength beyond resistance training alone.
Holwerda AM, van Loon LJC. The impact of collagen protein ingestion on musculoskeletal connective tissue remodeling: a narrative review. Nutrition Reviews. 2022;80(6):1497–1514.
Collagen supplementation on tendon-related structural and performance outcomes: a systematic review. Journal of Functional Morphology and Kinesiology. 2026;11(1):130.
NMN and longevity supplements
NMN reliably raises NAD+ levels in humans. That much is settled.
What has not been shown is that raising NAD+ produces meaningful health or longevity outcomes in people. The trials are short, small, and measure biomarkers rather than outcomes. Where benefits have appeared, they cluster in specific groups such as prediabetic women or trained runners, and may not generalise.
Worth noting for anyone who searches this. NMN's regulatory status has been unstable. The US FDA excluded it from the dietary supplement category in 2022 and reversed that position in late 2025. Europe is still assessing it. None of that is a safety finding, but it does tell you the category is unsettled.
Han K, et al. Nicotinamide mononucleotide (NMN) as a therapeutic agent for aging and age-related diseases. Biomedicine and Pharmacotherapy. 2024;172:116127.
Kim M, et al. Short-term effect of oral nicotinamide mononucleotide supplementation on clinical parameters in healthy middle-aged adults: a randomized, double-blind, placebo-controlled trial. Experimental Gerontology. 2024;187:112398.
Soluble fibre and cholesterol
Adding three grams or more of oat beta-glucan a day lowers LDL cholesterol by roughly 0.25 mmol/L and total cholesterol by about 0.30 mmol/L, without affecting HDL or triglycerides.
Viscosity is the mechanism, which is why the handbook names oats, barley and psyllium specifically rather than fibre in general. The thicker the gel it forms, the greater the effect.
Whitehead A, Beck EJ, Tosh S, Wolever TMS. Cholesterol-lowering effects of oat beta-glucan: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2014;100(6):1413–1421.
Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. American Journal of Clinical Nutrition. 1999;69(1):30–42.
The egg question
For most people, saturated fat raises LDL cholesterol more than dietary cholesterol does. The Heart Foundation's own position acknowledges that dietary cholesterol raises total and LDL cholesterol, but substantially less than saturated and trans fats do.
A 2026 randomised crossover trial from the University of South Australia put this directly to the test. Sixty-one adults rotated through three diets over five-week periods. Two eggs a day inside a low-saturated-fat diet actually reduced LDL cholesterol.
Which is the handbook's point. The butter on the toast is usually doing more than the egg beside it.
If you have high LDL cholesterol, type 2 diabetes or existing heart disease, this is a conversation for your GP or an Accredited Practising Dietitian rather than a general rule from a book. Your numbers and your overall risk change the answer.
Heart Foundation of Australia. Eggs and heart healthy eating: dietary position statement.heartfoundation.org.au
Effect of egg consumption within a low saturated fat diet on LDL cholesterol: a randomised crossover trial. American Journal of Clinical Nutrition. 2026.
Vitamin B12 on a vegan diet
In Australia, only plant milks, yeast extracts, meat and dairy analogues and energy drinks are permitted to add vitamin B12, at 0.2 to 2.0 micrograms per serve, and only if the manufacturer chooses to. Meeting the recommended intake generally takes two to three serves of fortified food a day.
In one Australian study of vegan participants, fewer than eleven per cent met the recommended B12 intake from fortified food alone.
This is why the handbook calls B12 non-negotiable rather than advisable.
Vitamin B12 supplementation adequacy in Australian vegan study participants. 2022.
Dietitians Australia. Vitamin B12 and vegetarian diets.
Iodine and seaweed
Seaweed can contain a lot of iodine. The problem is that the amount varies enormously, even within the same type of seaweed, and sometimes runs high enough to be a problem in the other direction.
That variability is why it cannot be relied on as your iodine source, and why eating more of it is not the fix.
Vitamin D comes mostly from sunlight
Most adults are unlikely to get more than five to ten per cent of their vitamin D requirement from food. For people in Australia and New Zealand, sunlight is the main source.
One clarification worth adding. Casual incidental sun exposure is not automatically enough, which is why the handbook points to current SunSmart guidance rather than suggesting you sort it out by accident.
Nowson CA, McGrath JJ, Ebeling PR, et al. Vitamin D and health in adults in Australia and New Zealand: a position statement. Medical Journal of Australia. 2012;196(11):686–687.
GLP-1 medications before surgery or sedation
The handbook tells you to disclose the medication to your treating team and follow their instructions. That advice has held steady while the specific protocols have moved considerably.
Australia now has joint recommendations from the Australian Diabetes Society, ANZCA, the Gastroenterological Society of Australia and the National Association of Clinical Obesity Services. The TGA also issued a medicines safety update in June 2025 requiring consideration of delayed gastric emptying and aspiration risk.
Because this guidance is still developing, check the current ANZCA page rather than relying on any protocol printed in a book.
Hocking SL, Scott DA, Remedios ML, et al. 2025 ADS/ANZCA/GESA/NACOS clinical practice recommendations on the peri-procedural use of GLP-1/GIP receptor agonists. Anaesthesia and Intensive Care. 2025;53(5):300–306.
ANZCA. Clinical practice recommendations regarding patients taking GLP-1 receptor agonists.anzca.edu.au
Australian guidelines used throughout
NHMRC Australian Dietary Guidelines
NHMRC Nutrient Reference Values for Australia and New Zealand
NHMRC Australian Guidelines to Reduce Health Risks from Drinking Alcohol
Cancer Council Australia and SunSmart UV guidance
Food Standards Australia New Zealand
Heart Foundation position statements
Dietitians Australia
Healthy Bones Australia
Butterfly Foundation
The NHMRC began a rolling review of the Nutrient Reference Values in 2019. If those figures change, this page and the next edition will change with them.
What has changed
1st Edition — 12/08/2026
First published.
Something wrong?
If you spot an error, an out-of-date guideline or a study we have missed, we would rather hear about it.
hello@thelongevitycoach.com.au