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Two different questions get argued as if they were one

One question is what a diet does to a body when the amount of food is held equal. The other is what happens when people are handed the rules and left to live. Those have different answers, and almost every argument about keto against vegan against carnivore is two people answering different ones at each other.

The Archive’s position

This is opinion, not a finding. Everything else on this page is the evidence.

Which diet you pick matters far less than whether you can keep eating it, and far less than whether it gets enough protein into you. Choose based on what you will still be doing in a year, not on a theory of how it works.

Why we hold it

  • The study that measured both directly found sticking to the diet was linked to weight loss at 0.60, and diet type at 0.07. Four diets built on clashing theories all worked about equally, and how well people stuck to them explained nearly everything.
  • When calories are matched in a hospital research unit, the differences shrink to almost nothing. Across 32 controlled feeding studies, the metabolic edge went to lower fat, not lower carbs, and it came to 16 grams of fat a day. That is a real measurement of a tiny effect.
  • When people are overfed at 5, 15 or 25% protein, fat gain is the same. What differs is lean mass. That is the same answer the protein research gives from the other direction, and it points at the same factor.
  • The two most serious attempts to predict who suits which diet, by genes and by insulin output, both failed, in a 609-person study built specifically to test them.
  • Every diet eaten freely that led to weight loss did it by cutting how much people ate, wherever intake was actually measured. The diets are delivery systems for eating less, and they differ in how pleasant that is to live with.

Where this goes beyond the evidence

The same for weight is not the same for everything, and this position is about body weight and body make-up, not health. At matched calories, the diets do differ steadily on cholesterol and blood fats, and in opposite directions. Cutting carbs lowers triglycerides and raises HDL while raising LDL, and cutting fat does the reverse. Those are real differences in measured risk markers, and nothing here settles what they mean for any one person. The long-term outcome evidence is also mostly from studies that only watch people. That means it is muddied by the fact that people who choose a diet differ from people who do not. And where two large studies of that kind have looked at the same question, they have sometimes flatly disagreed. Saying the diet barely matters for the scale is well supported. Saying it barely matters, full stop, is not, and we are not saying it.

Who this is not for

Anyone with a condition where a specific diet is a treatment rather than a preference. That includes diagnosed coeliac disease, established chronic kidney disease, or epilepsy managed on a keto diet. It also does not apply to anyone whose reason for choosing a diet is not body make-up at all.

Read the four trials this rests on

How to read any diet study in one table

Before the result, find out which of these four the study was. It changes what the number means more than anything else in the paper. It is usually in the methods section, not the headline.

Calories matched
Both groups ate the same number of calories, so a difference comes from what was in the diet, not how much people ate.
Ate freely
Both groups ate as much as they wanted. A difference here mixes the diet with how full it kept people and how well they stuck to it.
Told what to eat, reported it themselves
People were told what to eat and then said what they ate. People usually say they ate less than they did, so what each group really ate is unknown.
Tracked, not tested
Nobody was given a diet. People who choose a diet differ from people who do not in other ways too, so this shows a link, not a cause.

What the head-to-head studies found

  1. Weight loss tracked sticking to the diet, not which diet it was

    Who was studied

    160 overweight adults with high blood pressure, unhealthy cholesterol or high fasting blood sugar, assigned to Atkins, Zone, Weight Watchers or Ornish for a year

    Four diets built on clashing theories produced between 2.1 and 3.3 kg of loss at one year, with none clearly ahead. Weight lost was strongly linked to how well people said they stuck to their diet (a correlation of 0.60), and hardly at all to which diet they were given (0.07). Every diet cut the ratio of LDL to HDL cholesterol by around 10%.

    What this does not show

    That the diets are interchangeable for every purpose. Sticking to the diet was self-reported, which is a weak measure, and a one-year study cannot speak to what any of these does over decades.

    Study in peopleComparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial (2005)

  2. Overfed at 5%, 15% or 25% protein, everyone gained the same fat

    Who was studied

    25 healthy adults with steady weight, living in a hospital research unit for 10 to 12 weeks and overfed by about 954 calories a day for the final 8 weeks, with body make-up measured by DXA scan

    Total weight gain differed a lot, 3.16 kg on low protein against 6.05 and 6.51 kg. Body fat gain did not: it rose by similar amounts in all three groups. The difference on the scale was lean tissue, which the low protein group did not add at all. The authors put it flatly: calories alone explain the increase in fat.

    What this does not show

    What happens when eating less, which is the direction almost everybody cares about. This was overfeeding, in 25 people, in conditions nobody lives in.

    Study in peopleEffect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial (2012)

  3. Across 32 controlled feeding studies, cutting fat beat cutting carbs

    Who was studied

    A review that pooled 32 controlled feeding studies in which carbs were swapped for fat at the same calories

    People burned more energy, by 26 calories a day, and lost more fat, by 16 g a day, on the lower fat diets. That is the opposite of the popular claim that cutting carbs gives a metabolic edge.

    What this does not show

    Anything worth acting on either way. Sixteen grams of fat a day is a rounding error next to the differences that sticking to a diet makes. The honest reading is that the metabolic edge is real, measurable, and far too small to matter.

    Review of studiesObesity energetics: body weight regulation and the effects of diet composition (2017)

  4. Low fat against low carb for a year, and the two groups ended up eating the same

    Who was studied

    609 adults with a BMI of 28 to 40, assigned to a healthy low fat or healthy low carb diet for 12 months, with 22 group sessions and no calorie target given

    Weight change was 5.3 kg against 6.0 kg, a gap of 0.7 kg that could easily have been zero. The planned attempts to find who each diet suits both failed. A pattern of three gene variants did not predict who did better, and neither did how much insulin people made.

    What this does not show

    That matching a diet to the person is impossible, only that these two ways of trying it did not work. Both groups were also taught to eat whole foods and cut added sugar and refined grain, so this compares two good diets, not a good one against a bad one.

    Study in peopleEffect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial (2018)

One study to stop citing

KETO-CTA followed 100 people whose LDL cholesterol rose sharply on a keto diet. It reported that plaque growth in their arteries tracked the plaque they already had, not their ApoB (a blood measure of the particles that carry cholesterol). It was published in JACC Advances in 2025 under the title “Plaque Predicts Plaque, ApoB Does Not”. It spread fast because it seemed to answer the strongest objection to high-LDL keto diets.

It was withdrawn (retracted) in 2026, at the request of both the authors and the editors. Concerns were raised about how the study was done that affected how reliable the data was. The notice says the errors were too great to fix with a correction. PubMed now flags the original as a retracted paper.

It is still cited. That is the practical reason this page looks the way it does. A result that confirms what an audience already believes travels much further than the notice withdrawing it. Checking whether a paper still stands takes about thirty seconds. The retraction notice is here.

The patterns, one at a time

Each page reports the studies that matched calories apart from the ones where people ate freely. It names what the pattern reliably moves, including the test results its fans do not lead with, and says who it is wrong for.

Questions people ask about this

Is keto better than other diets for fat loss?
Not when calories are held equal. Across 32 feeding studies where researchers controlled the food, the small edge in body fat lost actually went to lower fat, not lower carb. It came to about 16 grams of fat a day. In everyday life, keto often does produce more weight loss. For some people it cuts appetite and is easy to follow. That is a real advantage, and a different one from the fat-burning claim usually made for it.
Why does the scale drop so fast in the first week of a low-carb diet?
Glycogen, the carbs your body stores, holds water: roughly three grams of water per gram of glycogen. So using it up drops scale weight fast without a matching change in fat. Studies that controlled the food and measured both found that cutting carbs caused more scale weight loss, while cutting fat caused more actual fat loss over the same period.
Does carnivore have trial evidence?
No study has put people on a carnivore diet and compared them with people on a different one. The published evidence in people is a survey of people who chose the diet themselves and stayed on it. That cannot separate the diet from the people it suits. That is a statement about the evidence, not a verdict on the diet.
Can I find out which diet suits my genetics?
The best-designed attempt to do this failed. DIETFITS picked two predictors in advance: a pattern in three gene variants, and how much insulin people make. It tested whether they could predict who would do better on low fat or low carb, in 609 people over a year. Neither predicted anything. Commercial tests making this claim are ahead of the evidence.
So does the pattern not matter at all?
It matters for things other than the scale. At matched calories, the patterns move blood fats such as cholesterol consistently, and in opposite directions. It also matters enormously for whether a person can actually live on it. What the studies undercut is the specific claim that one pattern melts fat faster than another at the same calorie intake.
How much proteinGLP-1s, muscle and hairFasting protocols