This is not medical advice. General information for self-tracking only. If you are under 18, pregnant or breastfeeding, have ever had an eating disorder or a difficult relationship with food, or have diabetes, heart disease, kidney disease or another medical condition, talk to a doctor or a registered dietitian before you change what you eat. If you take insulin or a medicine that can lower your blood sugar, do not cut carbohydrate without that conversation first. The numbers behind MyPlate's own targets are on the health sources page.

Why low carb seems to win in the first week

The oldest result here is also the one most likely to fool you. In 1976, six people with obesity spent ten days on each of three regimens, including an 800-calorie ketogenic diet and an 800-calorie mixed diet. They lost 467 grams a day on the ketogenic one and 278 grams on the mixed one.1

The authors then broke that loss down. Water made up 61% of it on the ketogenic diet and 37% on the mixed diet, while fat made up 35% and 60%. Multiply those through (the sums are mine, the percentages theirs) and fat loss comes to about 163 grams a day against about 165. The calories and the fat loss nearly matched, and the scale still showed far more on the ketogenic diet.

Part of the reason is glycogen, the carbohydrate you store in the liver and muscle, which is held with three to four parts water.2 Cut carbohydrate hard and you use up the store and lose the water with it. Eat carbohydrate again and it comes back, which is how one pasta dinner can seem to undo a week.

Six people and a 50-year-old method is thin evidence, and 800 calories was a clinical experiment rather than something to copy. Even so, I would not take a fast first week on low carb as evidence that it burns more fat.

What happened when researchers controlled every calorie

Asking people at home to eat a diet tells you what they did, not what the diet does. So Kevin Hall's group at the NIH locked the question inside a metabolic ward. Nineteen adults with obesity stayed as inpatients, exercised daily, and spent six days on each of two diets with the same calories, one cutting carbohydrate and one cutting fat.3

Cutting carbohydrate did what its advocates predict: fat burning went up and stayed up. Cutting fat did not change fat burning at all. Yet the body fat lost was 53 grams a day on the low-carb diet and 89 grams on the low-fat one, because eating less fat removes more fat from the balance than burning a little more makes up for. The same paper's modelling predicted the gap would shrink over a longer diet, so I would not read it as a reason to choose low fat. It is a reason to doubt that lower insulin automatically means more fat loss.

A second ward study ran longer and went further, moving 17 men from a 50% carbohydrate diet to a 5% ketogenic one at equal calories, for a month each.46 Body fat loss slowed on the ketogenic diet rather than speeding up, and the men were breaking down more protein and losing lean mass. The order was fixed, baseline first and ketogenic second, so the two months are not a clean comparison.

The 209-calorie result, and the argument it started

In 2018 David Ludwig's group fed 164 adults who had already lost 12% of their weight, on 60%, 40% or 20% carbohydrate for 20 weeks, holding protein fixed and adjusting calories to keep their weight steady.5 Total energy expenditure, measured with doubly labelled water, was 209 calories a day higher on the low-carb diet than the high-carb one (95% CI 91 to 326). The confidence interval sits well clear of zero. The authors also disclosed that Ludwig has received royalties from books recommending a low glycemic load diet.

The objection is about the instrument. Doubly labelled water does not measure calories directly: it measures carbon dioxide output, and converting that to calories needs an assumption about which fuel you are burning, which a diet like this changes. When Hall's team reworked the ketogenic ward data, the doubly labelled water method showed 209 extra calories a day, while the respiratory chambers, measuring the same men, showed 24 (not significant).6 Adjusted for energy balance, the water figure fell to 139 and stopped being significant. The authors concluded that uncorrected calculations "erroneously suggest" a substantial increase. It is a smaller trial, 17 men, on a far more extreme diet than Ludwig's.

Then each side published a meta-analysis. Hall and Guo pooled 32 feeding studies and found energy expenditure 26 calories a day higher and fat loss 16 grams a day greater on the lower-fat diets.7 Ludwig's group reanalysed 29 trials and argued that duration is the hidden variable. Most of those trials were very short, with a median of four days, and over the 23 shorter ones expenditure fell by 50 calories a day on low carb. Over the six longer ones it rose by 135 (95% CI 72 to 199).8 Their reading is that the body takes about two and a half weeks to adapt, and six trials is what that reading rests on.

Neither side is being careless. They disagree about a measurement and about which trials count, and I cannot referee that from a desk. What I can do is ask what it would be worth if Ludwig is right. His trial's trend was 52 calories a day per 10 points of carbohydrate, so moving from 45% to 30% would be about 78 calories, assuming that line holds outside a feeding trial, in people actively losing weight, which that trial did not test.

What happens when people eat these diets at home

If low carb carried a real metabolic edge, it should show up in long trials of ordinary people. A small edge does, and the reviews read it differently.

A Cochrane review of 61 trials and 6,925 people compared low-carbohydrate diets against balanced ones (45% to 65% carbohydrate). In people without type 2 diabetes, the low-carb group was 0.93 kg lighter at one to two years (95% CI 0.04 to 1.81, 14 trials), which the authors rated moderate certainty and called "probably little to no difference".9 They judged the risk of bias as predominantly high, mostly from missing outcome data. A 2015 meta-analysis that set low carb directly against low fat in weight loss trials found a slightly larger 1.15 kg in favour of low carb (95% CI 0.52 to 1.79).10

The biggest single trial is DIETFITS, with 609 adults and a 0.7 kg gap at a year that could have been zero.11 I have covered it in whether you need to track macros at all, which makes the wider case that calories decide the weight. So the honest size of the low-carb advantage at home is about a kilo, possibly nothing.

Can your insulin or your genes pick the diet for you?

The appealing version of this debate is that low carb suits some bodies and low fat suits others, and a test will tell you which. DIETFITS was built to check exactly that. It genotyped its participants and measured how much insulin they secreted after a glucose challenge. Neither the genotype pattern (P = .20) nor the insulin measure (P = .47) predicted who did better on which diet.11 In Ludwig's feeding trial, by contrast, the effect on expenditure was largest in the top third of insulin secretion, at 308 calories a day.5 One measured weight at home and the other expenditure under controlled feeding, so they do not strictly contradict each other, but nobody can use either to choose your diet today.

Then there is simply asking people. Surely a diet you chose beats one you were assigned? A trial of 207 veterans with obesity tested that directly, letting half pick low carb or low fat after hearing about their food preferences. At 48 weeks the people who chose had lost 5.7 kg and the people assigned had lost 6.7 kg, a difference that could be chance (95% CI for the difference -2.9 to 0.8 kg).12 The authors point out that these were older veterans offered only two diets, so it may not apply to you. I expected the opposite result, and it means "pick the one you prefer" is common sense rather than a finding.

The number that did predict weight loss

A two-year trial put 811 adults on four diets ranging from 35% to 65% carbohydrate, for two years. Weight loss at two years was 3.4 kg on the lowest-carbohydrate target and 2.9 kg on the highest. Satiety, hunger and satisfaction were similar across the diets. Attendance at group sessions was strongly associated with weight loss, at 0.2 kg per session.13

An earlier trial randomised 160 people to Atkins, Ornish, Weight Watchers or Zone. Weight loss correlated with how well people said they stuck to their diet (r = 0.60) and not with which diet it was (r = 0.07).14 Only 53% of the Atkins group and 50% of the Ornish group completed the year, so the two most extreme diets lost the most people. Both of these are associations, adherence was self-reported in the second, and people who are succeeding may be the ones who keep turning up. But they are the same signal from two directions, and they fit a gap of about a kilo between the diets themselves.

Where the two diets do differ: cholesterol

Weight is not the only thing these diets change, and this is where choosing low carb has a cost worth checking. A network meta-analysis of 121 trials and 21,942 people found that at six months low-fat diets lowered LDL cholesterol by about 7 mg/dL against usual diet, while low-carb diets lowered it by about 1 mg/dL. Low-carb diets raised HDL by about 2 mg/dL, and low-fat diets did not. The certainty was moderate for the low-fat LDL figure and low for the low-carb ones.15

That difference fades. By twelve months the same review found that most benefits for cardiovascular risk factors had essentially disappeared, except on the Mediterranean diet, and Cochrane found little to no difference in LDL at one to two years against balanced diets.9 A blood test tells you more about your own response than any of these averages. If you already have raised cholesterol or heart disease, that is a conversation for your doctor before you change your fat intake.

What the evidence does not settle

Whether low-carb diets raise energy expenditure past the first few weeks is open, and the published estimates run from slightly negative to a couple of hundred calories a day. It needs longer feeding trials with methods both sides accept. Those are expensive and rare.

Appetite is open too. The ketogenic argument is that low carb curbs hunger, but in an NIH inpatient study people ate 689 calories a day more on a ketogenic diet than on a low-fat plant-based one, for two weeks each, with one person withdrawing because of hypoglycemia on the low-carb arm.16 That was 20 people and it is hard to carry over to real life, where the two-year trial above found hunger similar across its diets.

And nobody has a validated way to predict which diet will suit you. Almost everything here also describes people with overweight or obesity, in high-income countries, for a year or two. Whether any of it holds over ten years, I cannot tell you.

How to keep tracking macros for weight loss on either diet

This table puts the splits in grams at an illustrative 1,800 calories. The carbohydrate and protein sums use 4 calories a gram and fat 9, the standard factors.17 The DIETFITS rows are what its participants averaged at twelve months, not a prescription.11

At 1,800 calories Carbohydrate Fat Protein
MyPlate's weight loss split (45/27/28)202 g54 g126 g
DIETFITS low fat, as eaten (48/29/21)216 g58 g94 g
DIETFITS low carb, as eaten (30/45/23)135 g90 g103 g

"Low fat" in DIETFITS was not extreme, and neither was "low carb" compared with what a keto plan asks for. The low-carb row does sit outside the ranges the National Academies give for adults (45% to 65% carbohydrate, 20% to 35% fat),18 which is why MyPlate does not produce it, and why I would treat it as a decision to make deliberately.

If you do try one, this is the order I would work in. These steps are my reading of the trials above, not a protocol anyone has tested.

  1. Set the calories first, since the split moved results by about a kilo in the home trials above. How to count calories covers the target. The NIH guidelines describe low-calorie diets of 1,000 to 1,200 calories a day for women and 1,200 to 1,500 for men,19 and MyPlate never sets a target below 1,200 for women or 1,500 for men.
  2. Swap carbohydrate and fat against each other, and leave protein where it is. DIETFITS and Ludwig's trial both kept protein close between arms, so the comparisons above say nothing about a diet that also drops protein. Why macro calculators disagree about protein covers how to pick that number.
  3. Do not judge the first two weeks. That is my rule of thumb from the water data rather than a trial result. Compare later weeks against each other, because the opening drop is the part you will not repeat, and read the trend the way the plateau post describes.
  4. Watch the fat you cannot see. On the low-carb row, 45% of your calories come from the macro with the most calories per gram, so 10 grams of unseen oil costs 90 calories where 10 grams of unseen carbohydrate costs 40. The oil in the pan is the usual culprit, and a photo will not show it.
  5. Decide after six months, not after one. In the two-year trial everyone had lost about 6 kg at six months, and regain began after a year.13 Ask whether you could still be eating this way then.

On what the app does: MyPlate gives every weight loss goal the same split, 28% protein, 45% carbohydrate and 27% fat, and it has no setting to change it. If you eat low carb, your carbohydrate bar will sit under target and your fat bar will run over, and neither of those is a problem. Use the calorie and protein numbers. A scan is also an estimate, so its carbohydrate and fat figures are less certain than a label's. If you want the carbohydrate count for a clinical reason, such as insulin dosing, use a label and a dietitian's plan rather than a photo.

If tracking macros is making you anxious, or you are logging to punish a meal rather than to understand it, stop and talk to a doctor or a registered dietitian. What the research says about who that is most likely to be is in can calorie tracking cause an eating disorder.

Common questions

Is low carb or low fat better for weight loss?

Neither by much. A Cochrane review found low-carbohydrate diets about 0.93 kg ahead of balanced diets at one to two years and rated that as probably little to no difference, and the largest single trial found a 0.7 kg gap between low carb and low fat that could have been zero.911 In another year-long trial, how well people stuck to the diet predicted weight loss and the type of diet did not.14

Does a low-carb diet make you burn more calories?

Possibly a little, and it is disputed. One 20-week feeding trial found 209 calories a day more on a low-carb diet during weight maintenance, while metabolic ward work suggests that method overstates the effect, and a pooled analysis of 32 feeding studies found the opposite direction.567 In trials at home, low carb came out about a kilo ahead.

Why did I lose so much weight in the first week of low carb?

Mostly water. In a small 1976 study, a ketogenic diet produced much more weight loss per day than a mixed diet with the same calories, but 61% of it was water, and fat loss per day was about the same.1 Glycogen is stored with three to four parts water, so using it up takes the water with it, and it returns when you eat carbohydrate again.2

Is tracking macros for weight loss worth it if the split barely matters?

Partly. Tracking calories and protein does most of the useful work, and if you are choosing between low carb and low fat the difference in weight is about a kilo at most. Logging carbohydrate and fat is mainly useful for seeing which foods you are actually eating, or for keeping to a split you have chosen for other reasons.

What is the best macro tracking app for a low-carb diet?

The best macro tracking app for strict low carb is one that lets you set your own targets and gives you exact label data. MyPlate does neither: its macro split is fixed at 28% protein, 45% carbohydrate and 27% fat for weight loss, it has no barcode scanner, and a photo scan is an estimate. It suits someone watching calories and protein on a loose low-carb diet, not someone counting grams for ketosis or for a medical reason.

Pick the one you can eat in month seven

A low-carb diet makes the scale look better early, mostly through water, and leaves you roughly a kilo ahead after a year or two.19 The fight over energy expenditure is real and I do not know how it ends. If you are tracking macros for fat loss, the choice comes down to which foods you can keep eating, and a blood test can tell you what your choice is doing to your cholesterol.

Sources

  1. Yang MU, Van Itallie TB (1976). Composition of weight lost during short-term weight reduction. Metabolic responses of obese subjects to starvation and low-calorie ketogenic and nonketogenic diets. Journal of Clinical Investigation, 58(3):722-730. Read on PubMed →
  2. Kreitzman SN, Coxon AY, Szaz KF (1992). Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition, 56(1 Suppl):292S-293S. Read on PubMed →
  3. Hall KD, Bemis T, Brychta R, et al. (2015). Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metabolism, 22(3):427-436. Read on PubMed →
  4. Hall KD, Chen KY, Guo J, et al. (2016). Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. American Journal of Clinical Nutrition, 104(2):324-333. Read on PubMed →
  5. Ebbeling CB, Feldman HA, Klein GL, et al. (2018). Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial. BMJ, 363:k4583. Read on PubMed →
  6. Hall KD, Guo J, Chen KY, et al. (2019). Methodologic considerations for measuring energy expenditure differences between diets varying in carbohydrate using the doubly labeled water method. American Journal of Clinical Nutrition, 109(5):1328-1334. Read on PubMed →
  7. Hall KD, Guo J (2017). Obesity energetics: body weight regulation and the effects of diet composition. Gastroenterology, 152(7):1718-1727. Read on PubMed →
  8. Ludwig DS, Dickinson SL, Henschel B, Ebbeling CB, Allison DB (2021). Do lower-carbohydrate diets increase total energy expenditure? An updated and reanalyzed meta-analysis of 29 controlled-feeding studies. Journal of Nutrition, 151(3):482-490. Read on PubMed →
  9. Naude CE, Brand A, Schoonees A, et al. (2022). Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk. Cochrane Database of Systematic Reviews, 1(1):CD013334. Read on PubMed →
  10. Tobias DK, Chen M, Manson JE, et al. (2015). Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis. Lancet Diabetes and Endocrinology, 3(12):968-979. Read on PubMed →
  11. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. (2018). 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, 319(7):667-679. Read on PubMed →
  12. Yancy WS Jr, Mayer SB, Coffman CJ, et al. (2015). Effect of allowing choice of diet on weight loss: a randomized trial. Annals of Internal Medicine, 162(12):805-814. Read on PubMed →
  13. Sacks FM, Bray GA, Carey VJ, et al. (2009). Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. New England Journal of Medicine, 360(9):859-873. Read on PubMed →
  14. Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ (2005). Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA, 293(1):43-53. Read on PubMed →
  15. Ge L, Sadeghirad B, Ball GDC, et al. (2020). Comparison of dietary macronutrient patterns of 14 popular named dietary programmes for weight and cardiovascular risk factor reduction in adults: systematic review and network meta-analysis of randomised trials. BMJ, 369:m696. Read on PubMed →
  16. Hall KD, Guo J, Courville AB, et al. (2021). Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nature Medicine, 27(2):344-353. Read on PubMed →
  17. Food and Agriculture Organization of the United Nations (2003). Food energy: methods of analysis and conversion factors. FAO Food and Nutrition Paper 77. Read the paper →
  18. Institute of Medicine (2005). Acceptable Macronutrient Distribution Ranges, in Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. The National Academies Press. Read the report →
  19. National Heart, Lung, and Blood Institute, NIH (1998). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. NIH Publication 98-4083. Read the guidelines →

The formulas and limits behind MyPlate's own numbers, with their citations, are on the health sources page.