In our chapter on hormesis, we saw that eating less—caloric restriction—is itself a hormetic stressor. Moderate stress makes the body stronger; push it too far and the bill lands on muscle and bone.
The last entry concluded that people who need to lose weight can eat 10%–15% less per day (by calories). The cost: in the CALERIE trial, healthy people who ate less for two years lost 7.5 kg, about 30% of it fat-free mass (muscle, water, and other non-fat tissue), and bone density fell at the lumbar spine and hip 1,2.
What we want to lose by eating less is fat. Muscle and bone should stay. This entry deals with that one problem.
Prime Diet 1.0 sets everyday protein at 1.2–1.5 g per kg of body weight, with whey after resistance training and a little casein before bed that night. That routine stays the same; this entry gives the version for when you are eating less or compressing your eating window.
Eating Less Costs Muscle, and Time-Restricted Eating May Cost a Little More
Pooling time-restricted eating trials without calorie targets: the time-restricted groups spontaneously ate 400-plus kcal less per day and lost 0.68 kg more lean mass than controls; in trials where both groups ate the same calories, no difference was detected 3. The extra lean-mass loss came together with eating less.
Two trials hint that the eating window itself may add a little. The US TREAT trial split 116 adults with overweight or obesity into two groups: one did 16:8 for 12 weeks (eating from noon to 8 p.m.), the other kept three regular meals. The 16:8 group did not lose more weight, but its appendicular lean mass index fell further (measured in 50 of the participants) 4. In a feeding trial in Wuhan, 96 adults with overweight or obesity all ate about 25% less; after 12 weeks the time-restricted group had lost 0.58 kg of lean mass, the unrestricted group 0.09 kg 5.
There are also opposite results. In a 12-month trial in Guangzhou, 139 people with obesity followed the same calorie-restricted meal plan; the group eating between 8 a.m. and 4 p.m. and the group eating at any time showed no detectable difference in lean mass 6.
Part of the weight lost by eating less is lean mass, including muscle; that much is certain. Whether time-restricted eating costs extra lean mass on top of eating less is inconsistent across trials, but it may cost a bit more. The countermeasures are the same either way.
Resistance Training Plus Enough Protein: In Most Trials, Lean Mass Held
Protein. Pooling 18 randomized trials, 14 comparisons made during caloric restriction showed that people who ate protein above the basic recommendation (0.8 g per kg) lost 0.36 kg less lean mass 7. In a far more extreme trial, 40 young men ate about 40% less and trained six days a week for four weeks (very extreme—please do not do this in daily life...). The group eating 2.4 g of protein per kg gained 1.2 kg of lean mass; the group eating 1.2 g gained 0.1 kg. They lost 4.8 kg and 3.5 kg of fat, respectively 8.
Training. In a trial of 160 adults over 65 with obesity, the dieting groups all lost about 9% of body weight over six months. Lean mass fell 5% in the group that added aerobic exercise and 2% in the group that added resistance training; hip bone density fell 3% and 0.5%, respectively 9.
Doing both. Forty resistance-trained women did eight weeks of supervised resistance training with protein at 1.6 g per kg; one group also compressed eating into about 7.5 hours a day. Fat-free mass rose 2%–3% in every group, with no difference between restricted and unrestricted eating 10. In 32 young women with overweight who ate 25% less and did resistance training for eight weeks, the two groups eating 1.6 g of protein per kg (one of which also practiced time-restricted eating) increased their fat-free mass 11. Pooling 15 studies of "time-restricted eating plus exercise," fat-free mass in the time-restricted groups showed no detectable difference from controls who only exercised 12.
The size of the deficit matters too. A pooled analysis found that once the calorie deficit reaches about 500 kcal a day, the lean-mass gains from resistance training are cancelled out on average (strength still improves) 13. The 200–400 kcal per day suggested in the last entry stays below that line.
Bottom line: with resistance training and protein done right, most trials found no extra loss of lean mass.
How to Eat Protein: The Total Matters More Than the Timing
Total. Across 49 trials and 1,863 people, alongside resistance training, gains in fat-free mass plateaued at a total protein intake of about 1.6 g per kg; above that, there was no further gain on average (an average relationship—individuals vary) 14.
Per meal. The muscle-building response to a single meal's protein also plateaus: per kg of body weight, at about 0.24 g in young men and about 0.40 g in older men 15. Older people need more per meal.
The one before bed. The long-term trial behind pre-sleep protein dates from 2015: 44 young men did 12 weeks of resistance training, and the group drinking 27.5 g of protein before bed each night gained more strength and more thigh-muscle cross-sectional area 16. But the control group drank a calorie-free placebo, so the supplement group ate an extra 27.5 g of protein a day. There is no way to tell whether the benefit came from "before bed" or from "more in total" (a systematic review also flagged the unequal protein intakes) 17. Pooling twenty-odd trials of protein before and after training, once total protein is accounted for, the difference made by timing is no longer significant 20. That total outweighs timing is consistent with the pre-sleep results.
Secure the total first, then make sure each meal has enough and that you eat at least three times a day. Do that, and the extra benefit of a pre-bed dose is small.
Can Your Kidneys Handle 1.6–2.0 g of Protein?
Does eating more protein hurt the kidneys? It is an important question. In a Korean community cohort of 9,226 people, the quarter with the highest protein intake had 3.5 times the risk of renal hyperfiltration as the lowest quarter, and a higher risk of rapid decline in eGFR (a core measure of kidney function; creatinine is the other). But this is an observational study, the abstract reports no absolute risks, and it cannot show cause and effect 21. So let's look more closely:
In people with normal kidney function, existing trials have not seen damage. Many short-term trials show that more protein raises the glomerular filtration rate 22. That means the kidneys are working harder, not that they are being damaged. As for whether long-term hyperfiltration harms the kidneys, the longest direct evidence is a two-year weight-loss trial: 307 adults with obesity were randomized to a low-carbohydrate, high-protein diet or a low-fat diet. Over two years the high-protein group had higher creatinine clearance, higher blood urea, and more urinary calcium, but no adverse changes in glomerular filtration rate, albuminuria, or fluid and electrolyte balance, and no new kidney stones 23.
And for people whose kidney function has already declined? The effect is clear. The Nurses' Health Study followed 1,624 women for 11 years. In women with normal kidney function (eGFR above 80), protein intake was not associated with changes in kidney function. In women with an eGFR between 55 and 80, every extra 10 g of protein a day meant an additional 1.69 mL/min decline in eGFR over 11 years—especially non-dairy animal protein 24.
Where the protein comes from also makes a difference. In a US cohort of 12,000 people followed for 23 years, the fifth eating the most red and processed meat had a 23% higher risk of chronic kidney disease than the fifth eating the least (about one in five people in the cohort developed CKD); nuts, legumes, and low-fat dairy were associated with lower risk 25. In a Singapore cohort of more than 60,000 people followed for 15 years, the quarter eating the most red meat had a 40% higher risk of end-stage kidney disease (951 cases in the whole cohort, about 1.5%); poultry, fish, eggs, and dairy showed no such association 26. Kidney guidelines recommend that people with stage 3–5 chronic kidney disease keep protein at 0.8 g per kg, and that everyone with kidney disease at risk of progression avoid going above 1.3 g. They set no upper limit for healthy people 27.
For people with normal kidney function, eating 1.6–2.0 g of protein while restricting calories caused no kidney problems in trials lasting a few months to two years. People whose kidney function has already declined should not use this amount. What about beyond two years? There are no data. So this is the amount we use while eating less, not a lifelong amount, and kidney function should be checked once a year.
What Prime Lab Recommends
These recommendations are for people currently eating less, including those using 16:8, 5:2, or other fasting patterns to do it. People whose weight and markers are normal and who are not eating less should follow Prime Diet 1.0's everyday protein amount; but anyone doing time-restricted eating should still follow points 2, 3, and 4.
1️⃣ Eat 1.6–2.0 g of protein per kg of body weight per day. That is about 96–120 g for someone weighing 60 kg and 112–140 g at 70 kg—25–35 g a day more than Prime Diet 1.0's everyday amount, roughly a palm-sized portion of fish or meat plus a glass of milk. People who are well above their target weight (BMI 28 or higher) should calculate from their target weight. Make room for the extra calories by trading out staples and snacks. This is a temporary increase for the period of eating less: once your markers are back to normal and you switch to maintenance, return to 1.2–1.5 g per kg.
Before you start, check the kidney section of your checkup report (creatinine, eGFR) and your urinalysis. If your eGFR is below 80, you have proteinuria, or you have diabetes or high blood pressure with kidney damage, don't use this amount; let your doctor decide (follow medical advice!). Favor fish, poultry, eggs, dairy, and soy as protein sources, and keep red meat to Prime Diet's one to two times a week. The Paradox of Protein: What Nourishes You May Also Age You covers the other side of protein: eating a lot of it long-term keeps growth signals switched on. That article's conclusions still apply on days when you are not eating less.
If your creatinine sits at the upper limit of normal and your eGFR has stayed at 80–89 for years: first make sure the readings are accurate. Retest creatinine after an overnight fast, with no cooked meat in the previous 12 hours and no hard training in the previous 48 hours, and add cystatin C and a first-morning urine UACR. Once the values are confirmed as stable and accurate, take the conservative side: keep total protein at Prime Diet's 1.2–1.5 g per kg rather than raising it to 1.6–2.0, and if you need to eat less, rely on resistance training to protect muscle. Keep red meat to no more than once a week and make fish, eggs, dairy, and soy your main protein sources. Recheck both measures every year, and see a nephrologist if they keep falling. This point is Prime Lab's inference from the conservative side; no trial has compared protein amounts in this group.
2️⃣ Split protein across at least three meals, each with no less than 0.3–0.4 g per kg. For someone weighing 60–70 kg, 20–30 g per meal is the floor; to reach the daily total, in practice that means 30–40 g per meal, or 25–30 g at each of three meals plus a 20–25 g snack.
3️⃣ If you practice time-restricted eating (such as 16:8), still eat three meals within the window, and put training inside the window. Taking an 8 a.m. to 4 p.m. window and a body weight of 65 kg as an example:
- 8:00 Two eggs, 250 mL of milk, a small bowl of oats (about 28 g of protein)
- 12:00 150 g of fish or chicken breast, 100 g of firm tofu, a bowl of mixed-grain rice, vegetables (about 45 g)
- 15:30 100 g of shrimp or pressed tofu, 200 g of unsweetened yogurt, a small handful of nuts (about 30 g)
That totals about 105 g, just reaching 1.6 g per kg. On training days, add a scoop of whey protein after your session to get close to 2.0 g per kg. Train before the first meal or between two meals, and the meal after training serves as your post-workout protein (training fasted versus fed showed no clear difference in strength or fat-free mass) 28. If you can only train after work, shift the whole window later on training days so that a meal falls within two hours of finishing. If your window is so short that you can only fit two meals, widen it to 10 hours.
Make the last meal at least 30 g of protein and include a dairy food (about 80% of the protein in milk and yogurt is casein). Prime Diet 1.0's habit of "casein before bed on training nights" still works for people eating three normally spaced meals: the benefit is small but harmless, so treat it as one more way to top up the daily total.
4️⃣ Do resistance training two to three times a week—two is the minimum—for 40–60 minutes each time. While eating less, the goal is to keep your strength, not to build muscle. For exercise choices and intensity, see Not Just Lifting: A Three-Dimensional Blueprint for Whole-Body Strength.
5️⃣ A mostly plant-based diet is fine, as long as the total is there. With protein at 1.6 g per kg or more and resistance training, fully plant-based and omnivorous diets build muscle equally well 29,30. Favor tofu, pressed tofu, and soy milk. People over 65 should add a portion of eggs, dairy, or fish to each meal 31.
6️⃣ Keep monitoring. Measure weight and waist once a week; log the weight and reps of every training session; measure muscle mass every three to six months on the same body-composition device at the same time of day; if you keep eating less for more than a year, add a bone-density scan; while your protein is raised, check kidney function (eGFR) and urine microalbumin once a year. If your weight is going down and your training weights are holding, you are on the right track. If your training weights slide for two or three weeks in a row, first make the calorie cut smaller, then check whether you are getting enough protein.
The next entry takes on a reason many people give for fasting: "After 16 hours without food, autophagy starts clearing out the junk." Where does that claim come from, and should you extend your fasts to get more autophagy?
References31
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