Low-Carb vs Low-Fat Diets: Which Works Better for Fat Loss?
For fat loss, low-carb and low-fat diets work about equally well when calories and protein are similar. Well-run trials comparing the two over a year have found small, inconsistent differences on average, with large differences between individuals within each group. What decides your result is the calorie deficit you can sustain and whether you can keep eating that way for months. Low-carb often produces a faster drop on the scale in the first couple of weeks, but much of that early loss is water, not fat. So the better diet is the one that suits your appetite, your routine and your training, with protein kept high either way.
That answer frustrates people who want a winner. It should be a relief: you are free to choose.
What each approach actually means
Neither term has a strict definition, which is part of the confusion.
- Low-carb usually means cutting back on bread, pasta, rice, potatoes, sugar and many snacks, and eating more meat, fish, eggs, dairy, vegetables and fats. At the extreme end is a ketogenic diet, which cuts carbohydrate low enough to change how the body fuels itself. Our piece on keto and strength training covers that specific case.
- Low-fat usually means trimming oils, butter, fatty meats, cheese, pastry and many processed foods, and building meals around lean protein, grains, fruit and vegetables.
Both cut out a lot of calorie-dense processed food. That shared effect probably explains much of why both work.
What the research shows
One of the better-known trials, DIETFITS, run at Stanford and published in JAMA in 2018, randomly assigned over 600 adults to a healthy low-carb or healthy low-fat diet for a year. Average weight loss was similar between the groups. Within each group, some people lost a great deal and some gained. The researchers also tested whether genetics or insulin levels predicted who would do better on which diet; they did not.
The broad conclusion from that and similar studies is consistent: when protein and calories are matched, the carb-to-fat split matters much less than whether people stick to the plan.
Why low-carb looks faster at first
The body stores carbohydrate as glycogen in muscles and the liver, and glycogen is stored with water. Cut carbohydrate sharply and that store shrinks over a few days, taking water with it. The scale can drop quickly. It is real weight, but it is not fat, and it returns when carbohydrate does. Our explainer on water weight covers why the scale moves so much week to week.
How to choose: a practical comparison
| Consider | Lower-carb may suit you if | Lower-fat may suit you if |
|---|---|---|
| Appetite | Bread and snacks trigger overeating | You feel full on large, high-volume plates |
| Food preferences | You love eggs, meat, fish and cheese | You love rice, pasta, potatoes and fruit |
| Training | Mostly lifting, moderate volume | Lots of hard cardio or high-volume sessions |
| Social life | Restaurants with good protein options | Family meals built around grains |
| Past experience | You did well on it before | You did well on it before |
The last row is the most reliable predictor most people have.
Training and carbohydrate
Strength training uses carbohydrate as a fuel. Many people on very low-carb diets notice that hard sessions feel flatter, particularly in the first few weeks. Moderate low-carb, where you still eat some carbohydrate around training, usually avoids that. If your sessions are short and focused on lifting, either approach can work well. If you also run, cycle or do lots of intervals, very low-carb tends to cost performance.
What matters more than the split
- A modest calorie deficit. Our guide to what a calorie deficit is explains it without jargon.
- Enough protein. It helps keep muscle and keeps you full, on either diet.
- Strength training. So the weight you lose is mostly fat, not muscle.
- Fibre and vegetables. For fullness and general health, whichever way you lean.
- Sleep and alcohol. Both have a large effect on appetite and food choices.
Common mistakes
Low-carb, high everything else
Fat is calorie dense. Cheese, nuts, oils and fatty meats add up fast. Low-carb does not mean unlimited.
Low-fat, high sugar
“Low-fat” products often replace fat with sugar. A low-fat diet built on processed foods rarely feels satisfying.
Switching every few weeks
Each change resets your habits. Pick one approach and give it at least eight to twelve weeks before judging it.
Cutting out fruit and vegetables
Strict low-carb plans sometimes cut fruit and starchy vegetables to near zero, losing fibre and nutrients. Most people do better keeping them.
A middle path that works for most people
In practice, most of the people I coach end up somewhere between the two camps, and it works well. A sensible version looks like this:
- Protein at every meal, as the anchor.
- Plenty of vegetables and some fruit every day.
- Carbohydrate portions sized to the day: a little more around training, a little less on rest days or desk-bound days.
- Fats from olive oil, nuts, oily fish and eggs, measured rather than poured.
- Highly processed snacks and drinks kept as occasional rather than daily.
Nothing is banned, which makes it far easier to keep going through holidays, client dinners and busy weeks.
Check with your GP first
If you have diabetes, take medication that affects blood sugar or blood pressure, have kidney or liver disease, are pregnant, or have a history of disordered eating, speak to your GP before making a significant change to how you eat. The NHS healthy weight pages are a sound general reference.
How we handle it in the studio
When clients start 1-1 personal training in Highgate, we do not prescribe a diet camp. We look at what you already eat, what you enjoy, how you train and how your week runs, then adjust from there. Protein first, then a deficit you can live with. The InBody scan helps us check whether the weight coming off is fat rather than muscle.
Questions we get asked
Is low-carb better for belly fat?
There is no good evidence that either diet targets belly fat specifically. Overall fat loss reduces it.
Does eating fat make you fat?
Not on its own. A sustained calorie surplus does, whatever it comes from.
Can I build muscle on a low-carb diet?
Yes, with enough protein and calories, though very low-carb can make hard sessions feel tougher.
Should I count macros?
Not necessarily. Many people do well with portions and protein at each meal. If you want to know how coaching fits around this, see the personal training page.
Book with The Highgate House
Ready to start training properly? Email us at [email protected] with the service and the day that suits you, and we will come back to you with times.
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The Highgate House, Archway Road, Highgate, London N6.
