Protein does more jobs than almost any other nutrient you eat. It builds and repairs muscle, carries oxygen, forms enzymes and hormones, and holds fluid where it belongs in your blood.
Most people in developed countries are not protein deficient in the clinical sense. But many eat less than is optimal for their age and activity level.
In this guide, we explain the signs you may be under-eating protein and how much you actually need.
Highlights
- The adult reference intake is 0.8 g of protein per kilogram of body weight per day, which is a floor rather than a target.
- Training changes the number. Gains from extra protein level off at around 1.6 g per kilogram per day.
- Age changes it too. People over 65 are advised to eat more than younger adults, not less.
- Severe protein deficiency causes swelling, hair and skin changes, and is a medical issue rather than a reason to buy a shake.
Signs you may be under-eating protein
1. You are hungry again soon after eating
Protein is the most filling of the three macronutrients in the short term. A meta-analysis of 49 studies found that protein reduced hunger and increased fullness after a meal, and moved the hormones behind those feelings: ghrelin down, GLP-1 and cholecystokinin up. If you are hungry an hour after lunch, the protein content of that lunch is worth looking at before your diet as a whole.
2. You crave sugary food in the afternoon
A meal low in protein and high in fast carbohydrate gives you a sharper glucose rise and fall than a balanced one, and the dip is when cravings for sugar or simple carbs usually arrive.
Adding protein to a snack is the simplest fix: a handful of nuts, a boiled egg, Greek yoghurt or cottage cheese in place of something purely carbohydrate.
3. You are not gaining strength from training
If you lift regularly and nothing is changing, protein intake is one of the first things to check.
In a review of 49 studies covering 1,863 people , protein supplementation during resistance training produced measurable gains in strength, fat-free mass and muscle fiber size. The same review found gains level off once total intake reaches about 1.6 g per kilogram of body weight per day, so there is a real range to aim at and a point past which more stops helping.
4. You are losing muscle as you get older
Muscle is the body’s largest protein store, and age makes it harder to maintain.
Older bodies extract more of the protein in a meal before it reaches the muscle and respond less strongly to what does arrive. The PROT-AGE study group therefore recommends that people over 65 eat at least 1.0 to 1.2 g per kilogram per day, which is above the general adult reference intake, and more than that if they are active.
5. You are slow to recover from illness
Recovery is a building process and it needs materials. PROT-AGE advises 1.2 to 1.5 g per kilogram per day for older adults managing acute or chronic illness, on the basis that inflammatory and catabolic conditions raise protein needs.
6. Your hair, skin and nails are in poor condition
Hair, skin and nails are largely structural protein, so they are sensitive to sustained shortfall. Thinning hair and brittle nails have many other causes, including iron deficiency and thyroid problems, so this is a reason to check those too rather than a protein diagnosis.
7. You feel flat and unfocused
Amino acids from dietary protein are the raw material for neurotransmitters including dopamine, noradrenaline and serotonin, so a sustained shortfall gives your brain less to work with.
The popular version of this goes further than the evidence does. Eating a high-protein meal does not reliably raise brain serotonin, because protein also raises the other amino acids that compete with tryptophan for the same route into the brain. Adequate protein matters for mood and focus. A single protein-heavy meal is not a mood intervention.
8. You are getting the recommended minimum and no more
The adult reference intake of 0.8 g per kilogram per day is set to prevent deficiency, not to optimize anything. For a 70 kg adult that is 56 g a day.
If you train, you are over 65, or you are recovering from illness, every source above puts your requirement higher than that floor. Hitting the minimum exactly is itself a sign you could use more.
How much protein do you actually need?
| Body weight | Minimum daily recommendation | Over 65 (1.0–1.2 g/kg) | Over 65, active or managing illness (1.2–1.5 g/kg) | Weight training (1.6 g/kg) |
|---|---|---|---|---|
| 50 kg (110 lb) | 40 g | 50–60 g | 60–75 g | 80 g |
| 60 kg (132 lb) | 48 g | 60–72 g | 72–90 g | 96 g |
| 70 kg (154 lb) | 56 g | 70–84 g | 84–105 g | 112 g |
| 80 kg (176 lb) | 64 g | 80–96 g | 96–120 g | 128 g |
| 90 kg (198 lb) | 72 g | 90–108 g | 108–135 g | 144 g |
| 100 kg (220 lb) | 80 g | 100–120 g | 120–150 g | 160 g |
| 110 kg (243 lb) | 88 g | 110–132 g | 132–165 g | 176 g |
| 120 kg (265 lb) | 96 g | 120–144 g | 144–180 g | 192 g |
Conclusion
Most people reading this are not protein deficient. A good number are eating the bare minimum while training, ageing or recovering, all of which raise the requirement above the floor.
Work out your own number from your weight and your situation, spread protein across the day rather than loading one meal, and treat swelling, skin changes or faltering growth as reasons to see a doctor rather than reasons to buy a supplement.
References
- 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. PMID 28698222 . 49 studies, 1,863 participants.
- 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. PMID 23867520
- Morell P, Fiszman S. Effect of short- and long-term protein consumption on appetite and appetite-related gut hormones, a systematic review and meta-analysis. Physiology and Behavior 2020;226:113123. PMID 32768415 . 49 acute and 19 long-term publications.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press, 2005. Source of the 0.8 g/kg/day adult reference intake.
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns and before undertaking a new healthcare regimen including making any dietary or lifestyle changes.
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