Signs of Low Protein Intake: What to Look For

The signs of low protein intake are swelling, muscle loss, fatigue and frequent infections. They belong to severe deficiency, which is tied to famine and scarce food. A mild shortfall may give no clear sign at all. The check that works is a number: under 0.8 g of protein per kg a day, or 56 g at 70 kg. I took the signs from MedlinePlus page on kwashiorkor and the 0.8 g/kg figure from a 2017 review in Advances in Nutrition.

What are the signs of low protein intake?

MedlinePlus lists these signs for kwashiorkor, the severe form of protein deficiency. They are swelling (edema), lost muscle mass, fatigue, changes in hair color or texture, skin changes and rash, irritability, diarrhea, and more frequent or severe infections. The page calls it rare in children in the United States. It is most common where food is scarce.

That is the severe end. For most adults the question is milder: am I a bit under, and would I know? You wouldn’t. Tiredness, thin hair and slow recovery have too many other causes. The sources I read give no checklist that picks out a mild protein shortfall. I’m not going to invent one.

Swelling, muscle loss you can’t explain, or infections that keep coming back are reasons to see a doctor, whatever your protein intake is. Low intake does happen, though. The same page cites a government estimate: as many as half of older people in US nursing homes don’t get enough protein.

How low is low protein intake?

Under 0.8 g per kg of body weight a day. That is the US Recommended Dietary Allowance. The Advances in Nutrition review explains how it was set: from nitrogen balance studies, 2 standard deviations above an average requirement of 0.66 g/kg. So the average adult needs about 46 g at 70 kg and the RDA covers almost everyone at 56 g. One day under 56 g isn’t a deficiency, but months of days like that could be.

Body weight	0.8 g/kg (US RDA)	1.2 g/kg (low end of the US goal)
55 kg (121 lb)	44 g	66 g
70 kg (154 lb)	56 g	84 g
90 kg (198 lb)	72 g	108 g

The 2025–2030 Dietary Guidelines for Americans set a higher goal of 1.2–1.6 g/kg, and the 2025–2030 dietary guidelines on protein intake goes through what the text says. They also name protein among the nutrients where vegan diets fall short, which matters if you eat no animal foods. Low can mean two things here: under the floor, or under the goal. I call under 0.8 g/kg low by any standard. Between 0.8 and 1.2 is above the floor and below the goal, which I’d treat as room to improve, not a problem.

Britain sets the floor a little lower. The British Nutrition Foundation protein page gives 0.75 g/kg, which it lists as 56 g a day for men and 45 g for women. Women can see the 2025–2030 range against body weight in daily protein intake for women.

Most adults clear the floor. In US survey data from 2007 to 2010, adults ate 82.3 g of protein a day on average. Men averaged 98.6 g and women 67.0 g. That survey is old and relied on 24-hour food recalls, so treat the averages as a rough guide.

Calories change the picture. MedlinePlus puts it at 10% to 35% of calorie needs, and a gram of protein supplies 4 calories. At 1,500 kcal a day, 10% is 37.5 g, well under the 56 g floor for a 70 kg adult. Eating little makes a low protein day easy even when the percentage looks fine.

Who is most likely to eat too little protein?

Older adults are the clearest case. The Health ABC study followed 2,066 people aged 70 to 79 for 3 years. Those in the highest fifth of protein intake lost about 40% less lean mass than those in the lowest fifth. It’s an observational study, so it shows a link, not a cause. Aging and protein intake lays out how thin the trial evidence is. The PROT-AGE study group recommends at least 1.0–1.2 g/kg for people over 65 and 1.2–1.5 g/kg for most older adults with acute or chronic disease.

Vegans are the second group, since the Guidelines list protein among the nutrients vegan diets fall short on. The day below shows a plant-based menu can still reach the number if you choose the foods on purpose.

The third is anyone eating very little. At 1,500 kcal, 15% of calories is 56 g, which is the whole floor for a 70 kg adult.

What does a low protein day look like?

Here is a day I built from ordinary foods for a 70 kg (154 lb) adult. Fully plant-based, with a USDA record linked on each row.

Meal	Food and grams	Protein	Energy
Breakfast	Rolled oats, dry, 80 g	10.8 g	303 kcal
Breakfast	Banana, 115 g	0.9 g	101 kcal
Lunch	Whole-wheat bread, 2 slices, 64.2 g	7.9 g	163 kcal
Lunch	Creamy peanut butter, 32 g	7.7 g	189 kcal
Lunch	Gala apple, 180 g	0.2 g	99 kcal
Snack	Raw almonds, 28 g	6.0 g	163 kcal
Dinner	Spaghetti, cooked, 248 g	14.4 g	392 kcal
Dinner	Marinara sauce, 135 g	1.9 g	61 kcal
Dinner	Broccoli, boiled, 78 g	1.9 g	27 kcal
Dinner	Olive oil, 13.5 g	0.0 g	119 kcal
Total		51.6 g	1,618 kcal

The day comes to 51.6 g of protein and 1,618 kcal. That is 0.74 g/kg, under the 56 g floor, and 13% of the day’s calories. Nothing in it is odd. Oats, bread, peanut butter and pasta carry the protein, while the fruit and olive oil carry almost none.

Three changes lift it into the US range.

Change	Protein	Energy
Add 2 large eggs at breakfast, 100.6 g	+12.5 g	+148 kcal
Swap the almonds for plain nonfat Greek yogurt, 156 g	+10.1 g	−68 kcal
Add 50 g of braised chicken breast at dinner	+16.1 g	+83 kcal
New day	90.2 g	1,780 kcal

The new day reaches 90.2 g, or 1.29 g/kg, inside the 1.2–1.6 g/kg goal. Without animal foods, use 198 g of boiled lentils at lunch (17.9 g of protein, 230 kcal). Add 126 g of firm tofu at dinner (21.8 g, 181 kcal). That gets the same day to 91.2 g.

What should I do this week?

Log three ordinary days with grams, then divide your average protein by your weight in kilograms. Under 0.8 is low. From 0.8 to 1.2 is above the floor. From 1.2 to 1.6 is the US goal, and how much protein you should eat a day explains where in that range to aim.

The protein calculator turns your height and weight into a range. Its floor is 60 g, and above that it follows the 1.2 to 1.6 g per kg range in the 2025–2030 Dietary Guidelines.

These numbers don’t apply to everyone. Kidney disease needs a target from your doctor, and pregnancy and breastfeeding change the figures too. This guide is written for adults 18 and over.

If counting calories has started to feel hard to stop, or eating feels out of control, talk to someone: ANAD in the US (1-888-375-7767), Beat in England (0808 801 0677), NEDIC in Canada (1-866-633-4220) or the Butterfly Foundation in Australia (1800 33 4673). If you’re in danger right now, call your local emergency number. Other UK numbers and crisis lines are on our crisis support page.

Instead of hunting for symptoms, divide. If your three-day average is under 0.8, the fix is one more serving of eggs, yogurt, fish, tofu or lentils. If it’s above, look elsewhere for the cause of how you feel, and ask a doctor.