How is this different from keto?

Ketosis. The Atkins starting phase, under about 20 g of carbs a day, is keto, and the program is built to move you out of it through three later phases. Most studies labelled low carb measure that later stage. In DIETFITS, the low carb group ended at 30 percent of calories from carbs. The practical difference is cholesterol. On this diet, LDL shows little to no change across 61 trials. On keto it rose in several studies and tracked blood ketone levels.

How much more weight will I lose than on a normal diet?

About a kilogram. Across 61 trials and 6,925 people, with calorie cuts set about the same in both groups in most of them, the difference was 1.07 kg at three to eight months and 0.93 kg at one to two years. In people with type 2 diabetes it was 1.26 kg and then 0.33 kg. The review's own summary is that there is probably little to no difference up to two years.

Then why do the six-month trials look so good?

Because at six months they are good. One study found 5.8 against 1.9 kg lost at six months, and another found 12.9 against 6.7 percent of body weight at 24 weeks. At twelve months the same people were at 5.1 against 3.1 kg, too close to call. And the first researcher to publish a big twelve-month win found no difference eleven years later, in a better-designed study. The early edge is real, and it does not last.

What actually improves and stays improved?

Triglycerides, and HDL. Triglycerides fell 20 percent against 4 percent at six months, and 0.84 against 0.31 mmol/L at 24 weeks. Those gaps held after accounting for the weight difference, in the studies that checked. HDL rose, or fell less than on the other diet, at every check in a two-year study. Those are the results this diet can claim with no catch.

Carbohydrate-restricted13 studies in people cited

Atkins and non-ketogenic low carbohydrate

Written by Aaron CuhaReviewed Sep 2026

Also called: Atkins, Low carb, Moderate carbohydrate restriction

A Cochrane review of 61 trials and 6,925 people found about one kilogram more weight lost than on a balanced carb diet at three to eight months, and about nine hundred grams at one to two years. Triglycerides and HDL move reliably. LDL does not move the way it does on keto, and that is the main practical difference between the two.

What it actually is

Cutting carbs without getting into ketosis, or without staying there. Atkins as written is a four-phase program. It starts with an induction phase under about 20 g of carbs a day, which is keto. Then carbs are added back week by week through three more phases, ending well above keto levels. Most of what the research calls Atkins or low carb measures that later stage, not the start. In A TO Z, the Atkins group was told to raise carbs after the first two months. In DIETFITS, the healthy low carb group was getting 30 percent of its calories from carbs at twelve months. In the Cochrane review that covers this ground, 42 of 61 trials studied carbs above 50 g a day or under 45 percent of calories, which is low carb and not keto. If your question is about ketosis, ketone testing, or LDL shooting up in some people, that is a different diet with different studies, and it has its own page on this site.

How its fans say it works

The carbohydrate-insulin argument, stated fairly: carbs raise insulin, insulin stops fat cells from letting go of their fat, and cutting carbs frees that energy and reduces hunger. This diet adds a second, weaker claim of its own. It says cutting carbs short of ketosis still improves triglycerides, HDL and blood sugar control, apart from any weight loss, so you get the benefit without the hard work of staying in ketosis. That second claim has been tested directly against keto, and it held up better than the first.

What happened when calories were controlled

Best kind of study available: 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.

With calories set the same, the difference against a balanced carb diet is about one kilogram at three to eight months, and it shrinks toward nothing by two years. The difference is real, and it is a kilogram. Where food was actually provided, rather than just prescribed, the metabolic edge runs the other way, by tens of calories a day.

A 2022 Cochrane review of 61 trials with 6,925 people is the anchor. In most of them, 45 of 61, both groups were given a similar calorie target or way of cutting back. In people without type 2 diabetes, low carb lost 1.07 kg more over three to 8.5 months, with a likely range of 0.59 to 1.55 kg. Over one to two years it was 0.93 kg more, with a likely range of 0.04 to 1.81 kg. The review rated both with moderate confidence and called both little to no difference. In people with type 2 diabetes, it was 1.26 kg more at three to six months and 0.33 kg at one to two years, a gap too small to be sure of. The bottom blood pressure number, long-term blood sugar (HbA1c) and LDL over one to two years also showed little to no difference.
The most common comparison in that review, in 24 of 61 trials, was a low carb, balanced fat, high protein diet (over 20 percent of calories from protein) against a diet balanced across carbs, fat and protein. So a big part of this evidence compares a higher protein diet with a normal protein diet and gives the credit to carbs.
POUNDS LOST put 811 adults on lower calorie diets with 65 percent or 35 percent of calories from carbs, for two years. Weight loss was 2.9 and 3.4 kg, not a real difference. Hunger, fullness and how happy people were with the diet were similar in all four groups. Each group session attended went with 0.2 kg more weight loss.
Hall and Guo 2017 pooled 32 tightly controlled feeding studies that swapped carbs for fat at the same calories. People burned slightly more energy (26 calories a day) and lost slightly more fat (16 g a day) on the lower fat diets. That is the opposite of a metabolic edge for cutting carbs, and the size is tiny either way.
Johnston 2006 is the study that separates this diet from keto. 20 adults ate strictly controlled amounts for six weeks. One group was in ketosis and one was not, on the same low carb intake, with ketosis checked by blood test. Weight loss was 6.3 against 7.2 kg, and fat loss 3.4 against 5.5 kg. Both leaned toward the non-keto group, but with only 20 people neither gap was big enough to rule out chance. What it does say is that nothing in the controlled data needs ketosis to get the results of cutting carbs.

What happened when people just ate it

When people eat on their own, low carb shows a real edge at six months that does not last to one year, and that pattern is strikingly steady across twenty years of studies. DIRECT cut calories, ran two years and had 84.6 percent of people sticking with it. It put low carb at 4.7 kg lost, Mediterranean at 4.4 and low fat at 2.9. A TO Z favoured Atkins at twelve months: 4.7 kg lost, against 1.6 for Zone, 2.6 for LEARN and 2.2 for Ornish, and only the Atkins against Zone gap was clear. Eleven years later the same researcher ran DIETFITS, which was larger and had better food quality in both groups, and found a gap of 0.7 kg, too small to be real. Foster 2010 ran two years with coaching in both groups. People lost about 11 kg at one year and 7 kg at two, with no difference between groups in weight, body make-up or bone density at any point. Bazzano 2014 favoured low carb by 3.5 kg at twelve months, a clear result. Samaha 2003 put 132 adults with severe obesity, 39 percent with diabetes, on low carb or low fat. At six months the low carb group had lost 5.8 kg against 1.9 kg, triglycerides fell 20 against 4 percent, and the body's response to insulin rose 6 percent against a 3 percent fall, all clear results. 79 of 132 finished. Stern 2004 followed the same people to one year: 5.1 against 3.1 kg, a gap of 1.9 kg that was too small to be sure of. 34 percent had dropped out, and the authors said people did not stick to the diet well. Triglycerides still fell more and HDL fell less on low carb. In the 54 people with diabetes, long-term blood sugar improved more, and these differences held after accounting for the weight difference. Yancy 2004 ran 120 overweight volunteers with high blood fats for 24 weeks and got the biggest gap in this research. 76 percent stayed in the low carb group, against 57 percent on low fat. Weight fell 12.9 against 6.7 percent. Triglycerides fell 0.84 against 0.31 mmol/L. HDL rose 0.14 mmol/L against a 0.04 fall. All of those were clear results, and LDL was not really different. Its own stated weak spot is the one to remember: the low carb group also got nutritional supplements that the low fat group did not, so the groups differed by more than carbs. Foster 2003 found a big six-month gap that came to nothing at twelve months.

Protein, and whether it muddies the result

Protein muddies this whole diet, and it is measured here better than anywhere else in this section. The Cochrane review says its most common comparison, in 24 of 61 trials, was a low carb, high protein diet (over 20 percent of calories from protein) against a diet balanced across carbs, fat and protein. Protein fills you up and protects muscle while you lose weight, all on its own. So a big share of the low carb research is measuring a protein effect and calling it a carb effect. The studies that held protein fixed, and the one that held carbs steady while changing only ketosis, found nothing. Where muscle was reported at all, the picture is mixed. Yancy 2004 found both groups lost far more fat than lean mass: 9.4 against 3.3 kg on low carb, and 4.8 against 2.4 kg on low fat. Foster 2010 found no difference in body make-up between groups at any point over two years.

The measured intakes behind the protein figures are on the protein page.

What reliably moves

Measure	Direction	From
Triglycerides (blood fats)	Down, and this is the most reliable effect of the diet	Down 20 against 4 percent at six months, and 0.84 against 0.31 mmol/L at 24 weeks, both clear results. It holds after accounting for the weight difference, in the studies that checked.
HDL (good) cholesterol	Up, or holding steady where the other diet's falls	Up 0.14 mmol/L against a 0.04 fall at 24 weeks, a clear result. At one year in a separate study, HDL fell less on low carb rather than rising, which is the same direction described differently.
LDL (bad) cholesterol	No steady change, and this is the difference from keto	Not really different at 24 weeks, and little to no difference over one to two years across 61 trials. On keto, LDL rose in some studies and tracked blood ketone levels. If you are choosing between the two on cholesterol, this is the difference that matters.
Body weight with the same calorie target	Down by about one kilogram more than a balanced carb diet	1.07 kg at three to 8.5 months and 0.93 kg at one to two years without diabetes, and 1.26 kg and 0.33 kg with it. Moderate confidence, across 6,925 people.
Body weight when eating freely, at six months	Down a lot more than low fat	3.9 kg more at six months in one study, and 6.2 percentage points of body weight more at 24 weeks in another. The gap closes or disappears by twelve months in almost every study that ran that long.
Long-term blood sugar (HbA1c)	Better in some studies of people with diabetes, and no different across the pooled evidence	Improved more in the 54 people with diabetes in one study, even after accounting for weight. Little to no difference against a balanced carb diet over one to two years across all the trials.
Staying in the study	Better in some studies, worse in others	76 against 57 percent finished one 24-week study, 34 percent dropped out of a one-year study, and another had poor sticking power and many dropouts in both groups. This is not a settled feature of the diet.

Long term, and serious health events

Two years is the limit, and by then the edge is about a kilogram or less. The Cochrane review puts it at 0.93 kg in people without type 2 diabetes and 0.33 kg in people with it, at one to two years. The bottom blood pressure number, long-term blood sugar and LDL all showed little to no difference over the same time. Its own conclusion is that there is probably little to no difference in weight loss or heart risk factors up to two years. No trial of this diet has counted heart attacks, broken bones or deaths. The long-term signal comes from studies that only watch people, and it goes against the meat-heavy version of this diet in particular. Fung 2010 followed 85,168 women and 44,548 men for 20 to 26 years. A low carb score built on animal foods carried a risk score of 1.23 for death from any cause, comparing the highest tenth to the lowest, where one means no difference. It was 1.14 for death from heart disease and 1.28 for death from cancer. A low carb score built on plant foods carried 0.80 for death from any cause and 0.77 for heart disease deaths. Seidelmann 2018 found a U-shaped curve in 15,428 adults over a typical 25 years, with the fewest deaths at 50 to 55 percent of calories from carbs. In a pooled look at 432,179 people, both under 40 percent (1.20) and over 70 percent (1.23) carried higher risk than a middle amount. In that analysis, swapping carbs for animal fat and protein gave a risk score of 1.18, and swapping them for plant sources gave 0.82. Two things have to be said about those numbers. These studies only watch people, with all the usual muddying factors. And a low carb score worked out from a food questionnaire, in a group where almost nobody was actually doing Atkins, is not the same thing as the diet. That is why they cannot settle the question either.

Sources

Review of studies2022
Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk.
Cochrane Database of Systematic Reviews
A review pooled 61 studies with 6,925 people; in 45 of them both groups were told to eat about the same calories. In people without type 2 diabetes, low carb gave 1.07 kg more weight loss at three to 8.5 months and 0.93 kg at one to two years. In people with diabetes the gaps were 1.26 kg and 0.33 kg. Blood pressure, long-term blood sugar and LDL (bad) cholesterol barely differed at one to two years.
61 randomised trials, 6,925 participants, energy prescription similar in both arms in 45 of them. Without type 2 diabetes: minus 1.07 kg at three to 8.5 months and minus 0.93 kg at one to two years. With it: minus 1.26 kg and minus 0.33 kg. Little to no difference in diastolic pressure, HbA1c or LDL over one to two years. The most common comparison was a high protein low carbohydrate diet against a macronutrient-balanced control, in 24 of 61 trials.
Study in people2003
A low-carbohydrate as compared with a low-fat diet in severe obesity.
New England Journal of Medicine
132 adults with severe obesity, 39 percent with diabetes, ate low carb or low fat for six months, and 79 finished. Low carb lost more weight, 5.8 kg against 1.9, and triglycerides fell 20 percent against 4. Insulin sensitivity rose 6 percent on low carb and fell 3 percent on low fat. The authors wanted long-term heart studies before backing the diet.
132 severely obese adults, 39 percent with diabetes, six months, 79 completed. Weight minus 5.8 against minus 1.9 kg (p = 0.002), triglycerides minus 20 against minus 4 percent (p = 0.001), insulin sensitivity plus 6 against minus 3 percent (p = 0.01). The authors called for long-term cardiovascular outcome studies before endorsing the pattern.
Study in people2004
The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial.
Annals of Internal Medicine
This followed the same 132 people to one year. Weight loss was 5.1 kg on low carb against 3.1 kg, a gap too small to rule out chance. Triglycerides fell more and HDL (good) cholesterol fell less on low carb, and long-term blood sugar improved more in the 54 with diabetes. 34 percent dropped out, and people did not stick to the diets well.
The one-year continuation of the same 132 participants. Weight minus 5.1 against minus 3.1 kg, difference minus 1.9 kg (95% CI minus 4.9 to 1.0), p = 0.20. Triglycerides fell more and HDL fell less on low carbohydrate; HbA1c improved more in the 54 with diabetes after adjustment. 34 percent dropout and suboptimal adherence.
Study in people2004
A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial.
Annals of Internal Medicine
120 volunteers with obesity and high blood fats ate keto-style low carb or low fat for 24 weeks. More stayed on low carb, 76 against 57 percent, and they lost 12.9 percent of body weight against 6.7. Triglycerides and HDL (good) cholesterol improved more on low carb, and LDL (bad) cholesterol did not clearly differ. The low carb group also got supplements the other group did not, which the authors named as a weakness.
120 volunteers, 24 weeks. Retention 76 against 57 percent (p = 0.02), weight minus 12.9 against minus 6.7 percent (p < 0.001), triglycerides minus 0.84 against minus 0.31 mmol/L (p = 0.004), HDL plus 0.14 against minus 0.04 (p < 0.001), LDL not significantly different (p = 0.2). The low carbohydrate arm also received nutritional supplements the comparator did not, which the authors name as a limitation.
Study in people2006
Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets.
American Journal of Clinical Nutrition
20 adults ate strictly controlled meals on low carb for six weeks, one group in checked ketosis and one not. The group not in ketosis lost a bit more: 7.2 against 6.3 kg of weight and 5.5 against 3.4 kg of fat, though neither gap was big enough to rule out chance. So you do not need ketosis to get the results of cutting carbs.
The trial that separates this pattern from the ketogenic one. 20 adults, six weeks, intake strictly controlled, ketosis verified. Weight 6.3 against 7.2 kg (p = 0.324) and fat loss 3.4 against 5.5 kg (p = 0.111), both favouring the non-ketogenic arm. Nothing in the controlled data requires ketosis to get the carbohydrate-restriction result.
Study in people2007
Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial.
JAMA
311 overweight women living normal lives followed one of four diets for twelve months; the Atkins group was told to add carbs back after the first two months. Weight loss was 4.7 kg on Atkins, 2.6 on LEARN, 2.2 on Ornish and 1.6 on Zone. Only the gap between Atkins and Zone was big enough to rule out chance.
311 free-living women, twelve months, with the Atkins arm instructed to increase carbohydrate after the first two months. Atkins minus 4.7 kg, Zone minus 1.6, LEARN minus 2.6, Ornish minus 2.2. Only Atkins against Zone reached significance.
Study in people2018
Effect 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.
JAMA
The same lead researcher ran this larger study eleven years later, with better food in both groups. The healthy low carb group got 30 percent of calories from carbs at twelve months, so it was not keto. The gap in weight loss between groups was 0.7 kg, too small to call real.
The same investigator, eleven years later, larger and with better diet quality in both arms. The healthy low carbohydrate arm reached 30 percent of energy from carbohydrate at twelve months, so this is a non-ketogenic trial. Between-group difference 0.7 kg (95% CI minus 0.2 to 1.6), not significant.
Study in people2003
A randomized trial of a low-carbohydrate diet for obesity.
New England Journal of Medicine
63 adults with obesity were put on low carb or a comparison diet for one year, with little help from staff. Low carb was well ahead at six months, but at twelve months the gap was 4.4 against 2.5 percent of body weight, too close to call. Both groups stuck to their diets poorly, and many dropped out.
63 adults, one year, minimal professional contact. A large six-month advantage narrowed to minus 4.4 against minus 2.5 percent of body weight at twelve months, p = 0.26. Adherence was poor and attrition high in both groups.
Study in people2010
Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial.
Annals of Internal Medicine
307 people followed low carb or low fat for two years, with coaching in both groups. They lost about 11 kg at one year and 7 kg at two, with no difference between diets in weight, body make-up or bone density at any point. HDL (good) cholesterol was higher on low carb at every check.
307 participants, two years, behavioural support in both arms. About 11 kg lost at one year and 7 kg at two, with no between-group difference in weight, body composition or bone mineral density at any time point. HDL was higher on low carbohydrate at every time point.
Study in people2014
Effects of low-carbohydrate and low-fat diets: a randomized trial.
Annals of Internal Medicine
148 adults followed low carb or low fat for twelve months. Low carb came out ahead: 3.5 kg more weight lost, a 1.5 percent bigger drop in body fat, and better triglycerides and HDL (good) cholesterol. The study did not count heart attacks or strokes.
148 adults, twelve months. Favoured low carbohydrate: weight minus 3.5 kg (p = 0.002), fat mass minus 1.5 percent (p = 0.011), triglycerides and HDL both better. No clinical cardiovascular endpoints.
Study in people2008
Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet.
New England Journal of Medicine
322 adults followed one of three diets for two years, and 84.6 percent stuck with it, the best in this set of studies. Weight loss was 4.7 kg on low carb, 4.4 kg on Mediterranean and 2.9 kg on low fat.
DIRECT. 322 adults, two years, 84.6 percent adherence, the best in this evidence base. Weight loss 4.7 kg low carbohydrate, 4.4 kg Mediterranean, 2.9 kg low fat.
Study in people2009
Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates.
New England Journal of Medicine
811 adults ate lower calorie diets for two years. Diets with 65 and 35 percent of calories from carbs led to 2.9 and 3.4 kg of weight loss, too close to call, and people felt about as full and hungry on each. Going to more group sessions predicted more weight loss, about 0.2 kg per session.
POUNDS LOST. 811 adults, two years, calories reduced in all arms. 65 percent against 35 percent of energy from carbohydrate produced 2.9 and 3.4 kg of weight loss, p > 0.20, with similar satiety, hunger and satisfaction. Session attendance predicted weight loss at 0.2 kg per session.
Study in people2010
Low-carbohydrate diets and all-cause and cause-specific mortality: two cohort studies.
Annals of Internal Medicine
This followed 85,168 women for 26 years and 44,548 men for 20 years. People whose low carb eating leaned on animal foods had higher death rates from all causes, heart disease and cancer. People whose low carb eating leaned on plant foods had lower death rates. It tracked what people said they ate, and a questionnaire score is not the Atkins diet.
85,168 women over 26 years and 44,548 men over 20. An animal-based low carbohydrate score carried all-cause mortality HR 1.23 comparing extreme deciles, cardiovascular 1.14 and cancer 1.28. A vegetable-based score carried 0.80 and 0.77. Observational, and a questionnaire score is not the Atkins diet.
Study in people2018
Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis.
Lancet Public Health
This followed 15,428 adults for about 25 years and pooled the results with studies of 432,179 people. Deaths were lowest when carbs made up 50 to 55 percent of calories, and higher under 40 percent or over 70 percent. Swapping carbs for animal fat and protein was linked to more deaths, and swapping for plant foods to fewer. It tracked what people ate, so it cannot prove cause.
15,428 adults over a median 25 years plus a meta-analysis of 432,179 participants. U-shaped relationship with lowest mortality at 50 to 55 percent of energy from carbohydrate. Under 40 percent HR 1.20 and over 70 percent HR 1.23. Exchanging carbohydrate for animal fat and protein gave 1.18; for plant sources, 0.82. Observational.

What people report

These are things people say about their own eating. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

Fast weight loss in the first one to two weeks, widely described, and widely understood in the community to be mostly water and stored carbs.
Appetite loss strong enough to skip meals. This is the most consistent report, and it is the reason the studies of people eating on their own support.
Triglycerides falling sharply on retest. This is the one blood test claim the study data backs without any catch.
LDL unchanged, which is what most people on the non-keto version report and what the trials show. A minority see it rise, usually during the stricter first phase.
Weight coming back during the phases where carbs are added back. This is reported very often, and it matches the studies, where the six-month edge is usually gone by twelve months.
No difference from any other diet, reported by people who had already cut calories before starting.
Constipation and low energy in heavy training. Both are common, both are blamed on low carbs, and neither was measured in these studies.
Trouble eating out and social friction, the most cited reason for stopping. It is less of a problem than on keto, because the later phases allow more carbs.

Sources: r/keto and low carb communities, the long-running Atkins program forums, and the data inside the studies on who stuck with it and who dropped out, which is unusually well reported here. 76 against 57 percent stayed in one study, 34 percent dropped out of another, and a third had poor sticking power and many dropouts in both groups. Unchecked self-report throughout.

Who this is wrong for

Anyone who came here with a keto question. This page is about cutting carbs without staying in ketosis. LDL shooting up in some people, the risk of a dangerous acid build-up on SGLT2 inhibitor diabetes drugs, and ketone testing all belong on the keto page.
Anyone on insulin or a sulfonylurea (a diabetes pill) without a prescriber involved. Blood sugar drops within days, fast enough to cause dangerous lows before anyone reviews the medicine.
Anyone with chronic kidney disease. The most studied version of this diet runs above 20 percent of calories from protein, and that protein load is a medical question for a kidney doctor, not a forum.
Anyone with an inherited cholesterol disorder. The average LDL change across 61 trials is little to none, but an average does not predict what happens to you. Get a cholesterol test before you start and about twelve weeks after.
Anyone expecting a big difference against a normal balanced diet. With calories set the same it is about one kilogram, and at one to two years it is about nine hundred grams.
Anyone building the diet around meat who takes the long-term data seriously. In two large studies that watched people, the animal-based version of a low carb score went with more deaths from any cause, heart disease and cancer, while the plant-based version went with fewer. No trial has tested that difference.
Anyone with a history of eating disorders. A phased program built on counting one food group every day is a poor fit.

Questions

How is this different from keto?: Ketosis. The Atkins starting phase, under about 20 g of carbs a day, is keto, and the program is built to move you out of it through three later phases. Most studies labelled low carb measure that later stage. In DIETFITS, the low carb group ended at 30 percent of calories from carbs. The practical difference is cholesterol. On this diet, LDL shows little to no change across 61 trials. On keto it rose in several studies and tracked blood ketone levels.
How much more weight will I lose than on a normal diet?: About a kilogram. Across 61 trials and 6,925 people, with calorie cuts set about the same in both groups in most of them, the difference was 1.07 kg at three to eight months and 0.93 kg at one to two years. In people with type 2 diabetes it was 1.26 kg and then 0.33 kg. The review's own summary is that there is probably little to no difference up to two years.
Then why do the six-month trials look so good?: Because at six months they are good. One study found 5.8 against 1.9 kg lost at six months, and another found 12.9 against 6.7 percent of body weight at 24 weeks. At twelve months the same people were at 5.1 against 3.1 kg, too close to call. And the first researcher to publish a big twelve-month win found no difference eleven years later, in a better-designed study. The early edge is real, and it does not last.
What actually improves and stays improved?: Triglycerides, and HDL. Triglycerides fell 20 percent against 4 percent at six months, and 0.84 against 0.31 mmol/L at 24 weeks. Those gaps held after accounting for the weight difference, in the studies that checked. HDL rose, or fell less than on the other diet, at every check in a two-year study. Those are the results this diet can claim with no catch.
Is a lot of it just the protein?: Probably a real part of it. The Cochrane review says its most common comparison, in 24 of 61 trials, was a low carb, high protein diet (over 20 percent of calories from protein) against a diet balanced across carbs, fat and protein. Protein fills you up and protects muscle on its own. So those studies measure protein and carbs together and report the result as carbs.