LCHF Diet vs Keto: What the Research Says

In short: An LCHF diet (low-carb, high-fat) cuts carbohydrates and gets most of its calories from fat; the ketogenic (keto) diet is its strictest form. Keto is a proven medical tool for some children with hard-to-treat epilepsy. For weight loss, an LCHF diet works about as well as other diets over a year, while it tends to raise LDL (“bad”) cholesterol and comes with some real side effects.

The LCHF diet and its stricter cousin, the keto diet, are some of the most talked-about ways to eat. Fans say they melt fat, kill cravings and sharpen your mind. Critics worry about cholesterol and long-term health. Here’s what the research actually shows, including where the evidence is strong, where it’s thin, and who should be careful.

What is an LCHF diet, and how is keto different?

“LCHF” is an umbrella term for any eating pattern that keeps carbohydrates low and makes up the difference with fat. Researchers usually call a diet “low-carb” when it has less than 130 g of carbohydrate a day (under 26% of calories on a 2,000-calorie diet), and “very low-carb” when carbs supply under 10% of calories [1]. On a 2,000-calorie diet, that’s about 50 g of carbohydrate a day or less.

A ketogenic diet sits at the very low end. With so little carbohydrate coming in, the liver starts turning fat into ketone bodies (beta-hydroxybutyrate, acetoacetate and acetone). These are small fuel molecules that the brain, heart and muscles can burn when glucose (blood sugar) is scarce. That metabolic state is called ketosis [2].

Not every LCHF diet is ketogenic. A moderate LCHF plan with, say, 80 to 120 g of carbs a day usually won’t keep you in ketosis, but it’s often easier to stick with. The medical “classic” keto diet used for epilepsy is far stricter: it’s built around a 4:1 ratio, meaning 4 g of fat for every 1 g of protein and carbohydrate combined [3].

Where keto started: epilepsy

Keto was a medical diet long before it was a weight-loss trend. A 2020 Cochrane review (an independent, high-quality summary of the research) pooled 13 randomized trials with 932 people who had drug-resistant epilepsy [3]. In children, ketogenic diets led to more seizure freedom and more seizure reduction than usual care. In adults, the evidence was much less certain, and no adult in those trials became seizure-free.

The review rated the evidence as low to very low certainty because the trials were small and couldn’t be blinded. Still, keto remains a recognized option for epilepsy that doesn’t respond to medication, and it’s done under close medical and dietitian supervision [3, 4]. That’s very different from trying keto on your own to lose weight.

Does an LCHF diet help weight loss?

Short answer: yes, about as well as other diets that cut calories, and maybe a little better in some studies. It’s not the fat-melting shortcut it’s often sold as.

One of the first randomized trials, published in 2003, put 63 adults with obesity on either a low-carb, high-fat diet or a conventional low-fat diet [5]. The low-carb group lost about 4% more of their body weight at six months, but the difference was no longer significant at one year. Adherence was poor and many people dropped out of both groups. A similar one-year trial in adults with severe obesity found the same weight loss on both diets, though the low-carb group had better triglycerides (a type of blood fat) and blood sugar control [6].

An early systematic review (a study that gathers and grades all the trials on a question) found that weight loss on low-carb diets was linked to eating fewer calories and staying on the diet longer, not to cutting carbs as such [7].

Later meta-analyses (studies that pool the results of many trials) found a small long-term edge for low-carb eating:

• Very low-carb keto diets led to about 0.9 kg (2 lb) more weight loss than low-fat diets after a year or more, in trials with around 1,400 people [8].
• Low-carb diets in general led to about 2.2 kg (under 5 lb) more weight loss than low-fat diets [9].

The biggest head-to-head trial so far, DIETFITS, randomized 609 adults to a healthy low-carb or healthy low-fat diet for a year [10]. They lost 6.0 kg and 5.3 kg, a difference too small to be meaningful. Neither genes nor insulin levels predicted who did better on which diet.

A tightly controlled NIH study adds another twist. Twenty adults lived on a research ward and ate as much as they wanted of either an animal-based keto diet or a plant-based low-fat diet, two weeks each [11]. They ate about 690 fewer calories a day on the low-fat diet. In other words, keto didn’t automatically make people eat less.

Does keto curb hunger?

A little. A meta-analysis found that people in ketosis felt slightly less hungry and had less desire to eat [12]. The main benefit seemed to be that ketosis stopped hunger from climbing as people lost weight, which usually happens on a diet. The changes were small, though, and the NIH ward study above shows that this doesn’t always translate into eating less.

The takeaway: the best weight-loss diet is the one you can keep up. If an LCHF diet helps you eat less without feeling deprived, it can work. If it leaves you miserable, a different approach will likely do just as well. Our guide to energy homeostasis explains why calorie balance still matters on any diet.

The LCHF diet and type 2 diabetes

This is where low-carb eating looks most promising. A 2021 meta-analysis in the BMJ pooled 23 trials with 1,357 adults with type 2 diabetes [1]. After six months, 57% of people on low-carb diets reached diabetes remission (defined as an HbA1c, a measure of average blood sugar, under 6.5%), compared with 31% on control diets. But when remission meant reaching that level without diabetes medication, the effect was smaller and not statistically significant. Most benefits for weight, triglycerides and insulin sensitivity had faded by 12 months, and the evidence was rated moderate to low certainty.

If you take medication for diabetes, cutting carbs can drop your blood sugar quickly, so doses may need adjusting. In the NIH study, one participant left the keto phase because of low blood sugar [11]. Talk to your doctor before you start.

Cholesterol and heart health

Low-carb diets have mixed effects on blood fats. On average they lower triglycerides and raise HDL (“good”) cholesterol, which is positive. But they also tend to raise LDL (“bad”) cholesterol [8, 9]. The average LDL rise is modest, but some people see much bigger jumps, so it’s worth getting a blood test a few months in.

Long-term studies that follow large groups of people raise further questions. A 2013 meta-analysis of observational studies linked a high low-carb diet score to a 31% higher risk of death from any cause [13]. A 25-year US study of over 15,000 adults, combined with seven other cohorts, found a U-shaped pattern: both very low and very high carb intakes were linked to higher mortality, with the lowest risk at around 50 to 55% of calories from carbs [14]. Crucially, low-carb diets built on animal fat and protein were linked to higher mortality, while low-carb diets built on plant foods like vegetables, nuts and whole grains were linked to lower mortality.

These are observational studies, so they show links, not cause and effect. People who eat low-carb may differ in other ways. Still, they suggest that what you eat on an LCHF diet matters. Olive oil, nuts, avocado, fish and vegetables are a better foundation than bacon and butter.

Keto for exercise and sport

For strength athletes, a short keto phase may be fine. In a small study of 8 elite gymnasts, 30 days of a very low-carb diet cut body fat without reducing strength or jump performance [15]. That could matter in weight-class sports, but eight people over one month is a very small sample.

Endurance is another story. In an Australian Institute of Sport study, elite race walkers trained hard for three weeks on either a high-carb diet, a “periodized” carb diet, or a keto LCHF diet [16]. The LCHF group burned far more fat, but walking at race pace took more oxygen. The two carb groups improved their 10 km race times by about 5 to 7%, while the LCHF group didn’t improve at all. If you train for speed or endurance, carbs still do important work. Our post on waxy maize starch looks at carbs around workouts.

Cancer, acne and mood: what we don’t know yet

Cancer. Because many tumors rely heavily on glucose, researchers have wondered whether keto could “starve” cancer. So far, human evidence is thin. A 2024 meta-analysis of randomized trials in adults with cancer found only eight trials, lasting 4 to 16 weeks [17]. Keto lowered blood glucose but didn’t clearly improve weight, quality of life or tumor-related markers, and the authors concluded there isn’t enough evidence to draw firm conclusions. Keto is not a cancer treatment. Anyone with cancer should only change their diet together with their cancer care team.

Acne. Diets with a high glycemic load (lots of fast-digesting carbs) have been linked to acne, and a 2012 review proposed ways keto could help [18]. That’s a hypothesis; we couldn’t find trials that actually tested keto for acne.

Mood and thinking. In a one-year Australian trial of 106 adults with overweight or obesity, people on a calorie-reduced low-fat diet ended up with better mood than those on a very low-carb diet with the same calories [19]. Working memory and processing speed were similar on both diets.

LCHF diet side effects and safety

• “Keto flu.” Many people report headache, tiredness, nausea, dizziness and “brain fog” in the first week or so. A study of posts in online forums found these symptoms usually peaked in the first week and faded within about four weeks [20]. That’s based on self-reports, not a clinical trial.
• Digestive upset. Constipation, vomiting and diarrhea were the most common side effects in the epilepsy trials [3]. Eating plenty of low-carb vegetables and drinking enough water can help.
• Kidney stones. A meta-analysis of 36 studies estimated that about 6% of people on long-term ketogenic diets developed kidney stones over an average of nearly four years (about 8% in the adult studies) [21].
• Higher LDL cholesterol in some people, as covered above [9].
• Hair shedding. Some people report it, but we couldn’t find good studies on hair loss from keto in healthy adults. If it persists, see your doctor.

Get medical advice before starting a strict LCHF diet if you take medication for diabetes or blood pressure, have kidney or liver disease, are pregnant or breastfeeding, or have a history of eating problems. If you’re curious about related products, our post on MCT oil, a fat often added to keto diets, looks at that evidence.

The bottom line on the LCHF diet

An LCHF diet is a legitimate way to eat, not a miracle. Keto has solid (if imperfect) evidence for drug-resistant epilepsy in children and promising short-term results for type 2 diabetes. For weight loss, it performs about as well as other calorie-reduced diets over a year, with a small edge in some analyses. It tends to raise LDL cholesterol, it can hurt endurance performance, and long-term observational data suggest that a plant-based version is a safer bet than one built on animal fat. If you try it, choose mostly whole, unprocessed foods, check your cholesterol, and involve your doctor if you have a health condition or take medication.

This article is for general information only and isn’t medical advice. Talk to your doctor or another qualified health professional before starting a new supplement. See our medical disclaimer.

References

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