The Protein Scaries: What the Research Says About Your Kidneys, Cancer, Bones, and Body Fat

How much cardio should you do, and does more of it ever become harmful? Cardiorespiratory fitness keeps improving with training load and nobody has found a ceiling. Getting fitter keeps lowering mortality risk as far out as anyone has measured. The one dose dependent harm that survives scrutiny is atrial fibrillation, and it shows up around six to seven hours a week of hard endurance training sustained for years.

How much resistance training do you actually need, and is there a point where more stops helping? We trace the "lift weights twice a week" recommendation back to the 1989 study it came from, which found that three days beat two, and to the citation loop that turned it into a guideline anyway. Then we go through the evidence on whether lifting is dangerous, including the heart, injury rates, and the J-shaped mortality curve, and work out where the dose-response actually saturates for strength, muscle mass, bone mineral density, and how your body handles fuel. The short answer is that almost every number in this literature marks where a benefit starts, and very little of it goes far enough to show where a benefit stops. We finish by writing the resistance training guideline the way we think it should be written, with target outcomes, a training dose, and testable targets.

Nearly every warning you've heard about lifting weights was written down before anybody checked it. We trace where those warnings came from, starting with a Harvard student in 1854 and ending with a curve on a graph that's being used today to argue you can lift too much. Along the way: the men who built themselves with barbells and then sold the public five-pound dumbbells, because iron was expensive to mail and a booklet cost pennies. The muscle-bound myth, which nobody could define when a graduate student surveyed 45 physiologists about it. The 1961 report that took the deep squat out of every branch of the American military, measured with a device its author built himself and never validated. The claim that lifting stunts a child's growth, which no professional body ever actually made. And the argument women got, which was never about injury at all.

Parts of the country now get a few weeks of wildfire smoke every year, and the obvious question is whether there is a point where the air is bad enough that the workout costs you more than it gives you. We went and looked. There is a real number, it comes from about 1.5 million people, and it is not the number that gets quoted. This is a free preview of Direct Line, our monthly ask-us-anything for Barbell Medicine Plus subscribers. Two of this month's twelve questions are here in full. First: training in wildfire smoke. What PM2.5 is, why the AQI on your phone and the number in the paper are not the same quantity, where the 90-minutes-at-100-micrograms figure comes from and why it is softer than it sounds, what happened when six cities modeled telling people to stay inside, and why your breathing rate during a set of squats matters more than you would think. Second: the effective reps model. A subscriber noticed that if a set only counts when you are within five reps of failure, the triceps in a heavy bench press should not count, and if you are going to count that as a fractional set for the triceps, then a warm-up set counts for the chest. Both cannot be true. We go through the meta-regression on proximity to failure, the 67-study analysis that tested whether an indirect set should count as one, as half, or as zero, and where we actually put our sets.

Most lifters have been told they need to eat in a Calorie surplus to build muscle. That rule has always come with a list of exceptions: unless you're new, unless you're carrying extra body fat, unless you're coming back from time off. Dr. Eric Helms joins Dr. Jordan Feigenbaum to work out what the rule is actually tracking, starting from a question with a real number attached: what does a pound of muscle cost to build? And then, do you need to be in a surplus to build muscle? Timestamps: 0:00 The rule, and its exceptions 2:08 Where "you need a surplus" came from 7:12 Heuristics versus theories 11:40 Hypertrophy, maintenance, deficit and surplus defined 14:58 Body fat as a savings account 18:24 How fast anyone can actually build muscle 23:39 What sets the ceiling: stimulus, not genetics 26:37 Microgravity, astronauts, and a 20 kg barbell 31:49 What constrains growth if steroids don't break the ceiling 36:44 If training sets the ceiling, what does energy do 38:45 What 1 kg of muscle costs to build 44:05 Why 3,500 Calories doesn't tell you what to eat 44:55 REDs and the dual intervention model 47:51 The 2000s bulking studies 51:34 Garthe 2013: elite athletes and a 500 Calorie surplus 58:30 Protein: 1.6 versus 2.5 g/kg 1:03:31 What starvation research shows the body protects 1:10:29 Vargas-Molina: maintenance versus deficit 1:19:17 What to do if you're lean 1:39:34 What would prove this wrong 1:57:57 Three buckets