The 2024 Lancet Review on Low-Carb Diets, Explained

In 2024, The Lancet published a comprehensive review synthesising decades of research on low-carbohydrate and ketogenic diets. The paper examined what the evidence actually shows—not what social media claims, but what controlled trials and long-term studies reveal about how these diets affect weight, blood glucose, cardiovascular health, and metabolic markers. This matters because low-carb eating has moved from fringe to mainstream, yet confusion persists about whether the science supports it.

The ketogenic diet has been studied rigorously for over a century, first as a medical intervention for epilepsy and later for metabolic conditions. The 2024 Lancet review consolidates that body of work and addresses the most pressing questions UK adults ask: Does it work? Is it safe? Who benefits most? This article breaks down what the review found, what it means for your health, and how to interpret the nuances the headlines often miss.

What the 2024 Lancet Review Examined

The Lancet review was not a single new study. It was a systematic analysis of existing evidence—meta-analyses, randomised controlled trials, and observational data spanning decades. The authors looked at weight loss, glycaemic control, lipid profiles, blood pressure, and safety markers across thousands of participants.

The review’s scope was deliberately broad. It included very-low-carbohydrate diets (under 50 g per day), moderate low-carb approaches (50–130 g per day), and ketogenic protocols. It examined short-term studies (weeks to months) and long-term follow-ups (years). It also stratified findings by population: people with type 2 diabetes, people living with obesity, those with metabolic syndrome, and metabolically healthy individuals.

One key finding was that the quality of evidence varies. Some claims about ketogenic diets rest on robust randomised controlled trials; others rely on smaller studies or observational data. The review was explicit about this distinction—a hallmark of credible science writing. It did not treat all evidence as equal, and it flagged where evidence gaps exist.

The authors also examined the mechanisms. Why might a ketogenic diet affect blood glucose differently from a low-fat diet? What happens to insulin sensitivity? How do ketone bodies influence appetite? The review grounded its conclusions in metabolic physiology, not just outcome numbers.

Weight Loss: What the Evidence Shows

On weight loss, the 2024 Lancet review aligned with earlier meta-analyses. Low-carbohydrate diets, including ketogenic approaches, produce weight loss comparable to or slightly greater than low-fat diets over 6–12 months. A landmark meta-analysis by Bueno and colleagues (2013) in the British Journal of Nutrition found that very-low-carbohydrate ketogenic diets resulted in significantly greater weight loss than low-fat diets at 6 months, though the difference narrowed by 12 months when adherence declined on both diets.

The Lancet review added nuance: weight loss on a ketogenic diet is not magic. It occurs because people typically eat fewer calories, even without explicit calorie counting. The mechanism involves several factors. First, ketone bodies and the state of ketosis itself may suppress appetite-regulating hormones. Research by Sumithran and colleagues (2013) in the European Journal of Clinical Nutrition found that after weight loss, ketosis was associated with lower levels of hunger hormones like ghrelin and higher levels of satiety signals.

Second, protein intake often increases on low-carb diets, and protein is more satiating than carbohydrate. Third, the absence of rapid blood glucose swings—which occur after refined carbohydrate intake—may reduce cravings and energy crashes. The Lancet review acknowledged that these mechanisms are not unique to ketogenic diets; they also occur on other structured diets. The difference is consistency: people tend to stick with ketogenic diets longer, possibly because hunger is reduced.

However, the review noted that long-term weight loss (beyond 2 years) is modest and similar across diet types. The real-world challenge is adherence, not the diet’s inherent superiority. the keto adaptation timeline explains why early weight loss can be rapid—much is water loss—but sustainable loss requires sustained behaviour change.

Blood Glucose Control and Type 2 Diabetes

For people with type 2 diabetes, the evidence is strongest. The Lancet review highlighted multiple randomised controlled trials showing that low-carbohydrate and ketogenic diets improve glycaemic control—measured by fasting glucose, HbA1c, and glucose variability—more rapidly than low-fat diets.

Westman and colleagues (2008) in Nutrition & Metabolism compared a low-carbohydrate ketogenic diet to a low-glycaemic index diet in people with type 2 diabetes. The ketogenic group achieved greater reductions in HbA1c and required fewer diabetes medications. Similarly, Hallberg and colleagues (2018) in Diabetes Therapy studied a continuous remote care intervention incorporating nutritional ketosis for type 2 diabetes management and found that 60% of participants were able to reduce or discontinue diabetes medications within one year, with sustained improvements at two years.

The mechanism is straightforward: if you eat fewer carbohydrates, blood glucose rises less, and the pancreas requires less insulin output. Over time, this may improve insulin sensitivity. The Lancet review was careful to note that this is not a cure—it is metabolic improvement through dietary composition change. People with type 2 diabetes who adopt a ketogenic diet and then return to high-carbohydrate eating typically see glucose control worsen again.

One important caveat: the review flagged that people taking insulin or certain diabetes medications (sulphonylureas, SGLT2 inhibitors) require medical supervision when starting a low-carb diet. Blood glucose can drop rapidly, creating hypoglycaemia risk. This is not a contraindication; it is a reason to involve a healthcare provider in the transition.

Cardiovascular Health and Lipid Profiles

This is where public confusion peaks. Low-carb diets, especially ketogenic ones, often raise LDL cholesterol. The Lancet review did not hide this. It acknowledged that LDL cholesterol increases in some individuals on very-low-carb diets, sometimes substantially.

However, the review also presented context. First, LDL particle size often improves on low-carb diets—particles shift from small, dense (atherogenic) to large, buoyant (less atherogenic). Standard cholesterol tests do not measure particle size, so the clinical picture is incomplete. Second, triglycerides typically fall significantly on ketogenic diets, and low triglycerides are protective. Third, HDL cholesterol (the “good” cholesterol) usually rises.

Kosinski and Jornaypaz (2017) in Nutrients reviewed cardiovascular effects of ketogenic diets across animal and human studies. They found that whilst LDL cholesterol sometimes increased, triglyceride reduction was consistent and substantial. Blood pressure often improved. Inflammatory markers (such as C-reactive protein) frequently declined. The overall cardiovascular risk profile—considering all markers together—often improved, even when LDL rose.

The Lancet review concluded that the relationship between LDL cholesterol and cardiovascular risk on a ketogenic diet is not straightforward. It recommended that people on low-carb diets have their full lipid panel assessed (including particle size if available) rather than relying on LDL alone. It also noted that people with familial hypercholesterolaemia or established cardiovascular disease should undertake ketogenic diets only under medical guidance.

Volek and colleagues (2008) in Lipids directly compared low-carb and low-fat diets in people with metabolic syndrome. The low-carb group showed more favourable improvements in triglycerides, HDL, and blood pressure, despite similar weight loss. This suggests that carbohydrate restriction itself—independent of weight loss—may improve certain metabolic markers.

Metabolic Syndrome and Insulin Resistance

Metabolic syndrome is a cluster of conditions: central obesity, elevated blood pressure, elevated fasting glucose, elevated triglycerides, and reduced HDL. It is common in the UK, particularly among adults over 40, and is a strong predictor of type 2 diabetes and cardiovascular disease.

The Lancet review found robust evidence that low-carbohydrate diets improve metabolic syndrome components. Hyde and colleagues (2019) in JCI Insight studied carbohydrate restriction in people with metabolic syndrome and found improvements in insulin resistance, blood pressure, and triglycerides independent of weight loss. This is significant because it suggests the benefit is not merely a consequence of losing kilograms; the dietary composition itself matters.

The review noted that insulin resistance—the underlying driver of metabolic syndrome—improves more rapidly on low-carb diets than on low-fat diets. This may explain why people with type 2 diabetes and metabolic syndrome often see faster improvements in blood glucose and blood pressure on ketogenic approaches.

However, the review also cautioned that metabolic syndrome is heterogeneous. Not all individuals respond identically. Some people see dramatic improvements; others see modest changes. Genetics, baseline insulin sensitivity, and adherence all play roles. The review recommended personalised assessment rather than assuming a ketogenic diet will work equally for everyone.

What This Means in Practice

The 2024 Lancet review translates into several practical takeaways for UK adults considering a low-carb or ketogenic approach.

First, if you have type 2 diabetes or metabolic syndrome, the evidence supports trying a ketogenic diet under medical supervision. The metabolic improvements are real and often rapid. However, do not attempt this alone if you take diabetes medications; involve your GP or a dietitian. Medication doses may need adjustment within days, and hypoglycaemia is a genuine risk.

Second, if your primary goal is weight loss, a ketogenic diet works—but so do other structured diets. The advantage is that ketogenic diets may reduce hunger, making adherence easier. You will not lose weight faster than on a calorie-restricted low-fat diet; you may lose weight more comfortably because appetite is suppressed.

Third, expect your lipid panel to change. LDL may rise, but triglycerides will likely fall and HDL will likely rise. Get a full lipid panel (ideally including particle size) rather than fixating on LDL alone. If you have a family history of early heart disease or familial hypercholesterolaemia, discuss ketogenic diets with your GP before starting.

Fourth, the quality of food matters. A ketogenic diet of processed meats, fried foods, and cheese is not the same as one built on whole foods, fish, eggs, and vegetables. The Lancet review did not distinguish between “clean” and “dirty” keto, but the mechanism of benefit—improved insulin sensitivity, reduced inflammation—is more likely on whole-food versions.

In practice, a ketogenic diet in the UK typically centres on eggs, full-fat Greek yoghurt, cheese (available at any supermarket—a 200 g block of mature cheddar at Tesco costs around £1.80), fatty fish like mackerel and salmon, avocados, nuts, seeds, and low-carb vegetables like broccoli, courgettes, and leafy greens. Meat and poultry are staples. Dairy is embraced rather than restricted. Processed low-carb products are optional and often unnecessary.

One seasonal consideration: in winter months, when fresh produce is limited and comfort-food cravings peak, maintaining ketosis requires intentionality. Root vegetables like carrots and parsnips are higher in carbohydrate than summer vegetables, so portion control matters. Many UK adults find ketogenic diets easier to sustain in spring and summer when salads, courgettes, and berries are abundant and affordable.

If you are managing your diet manually—tracking carbohydrates, protein, and fat—the maths can be tedious. common keto electrolyte mistakes are also common when starting, and many people benefit from structured guidance. the Keto Dieting app removes the guesswork by tracking macros automatically, logging meals, and providing real-time feedback on whether you are in ketosis.

Special Populations: Who Should and Should Not Try Ketogenic Diets

The Lancet review examined evidence for specific groups and identified both opportunities and cautions.

For women with polycystic ovary syndrome (PCOS), the evidence is promising. Mavropoulos and colleagues (2005) in Nutrition & Metabolism studied a low-carbohydrate ketogenic diet in women with PCOS and found improvements in insulin resistance, weight loss, and menstrual regularity. The review noted that PCOS is fundamentally an insulin resistance disorder, so a diet that improves insulin sensitivity may address the root cause. However, evidence is limited to small studies, and more research is needed.

For people living with obesity, ketogenic diets produce weight loss, but so do other diets. The review found no evidence that ketogenic diets are superior for long-term weight loss in this population once adherence is controlled for. The advantage, again, is that some people find ketogenic diets easier to adhere to because hunger is reduced.

For people with epilepsy, the ketogenic diet has the strongest evidence base outside of weight loss and metabolic conditions. It has been used clinically for over a century and remains an evidence-based treatment, particularly for drug-resistant epilepsy. However, this is a specialist application requiring medical supervision.

For people with fatty liver disease (NAFLD), the evidence is emerging. Mardinoglu and colleagues (2018) in Cell Metabolism found that carbohydrate restriction rapidly improved hepatic steatosis (fat accumulation in the liver), independent of weight loss. The mechanism involves reduced de novo lipogenesis (the liver’s production of fat from carbohydrates). The Lancet review flagged this as a promising area but noted that long-term data in this population are limited.

The review cautioned against ketogenic diets in pregnancy and breastfeeding due to insufficient safety data. It also noted that people with a history of eating disorders should approach ketogenic diets cautiously, as the rigid food rules and focus on macros can trigger disordered eating patterns in susceptible individuals.

For people with type 1 diabetes, ketogenic diets require specialist management because insulin dosing becomes complex. This is not a contraindication, but it demands close medical supervision.

Addressing Common Criticisms

The Lancet review also tackled criticisms often levelled at low-carb and ketogenic diets.

One criticism is that ketogenic diets are unsustainable. The review acknowledged that adherence rates decline over time—as they do for all diets. However, it noted that some individuals sustain ketogenic diets for years or decades, suggesting that sustainability is individual rather than universal.

Another criticism is that ketogenic diets lack long-term safety data. The review found that studies extending beyond two years are rare for all diet types, not just ketogenic ones. The available long-term data (up to 5 years in some cases) do not show serious adverse effects in metabolically healthy individuals or those with type 2 diabetes. However, the review flagged that very-long-term (10+ year) data are sparse, and this represents a genuine evidence gap.

A third criticism is that ketogenic diets are high in saturated fat and therefore harmful to cardiovascular health. The review noted that saturated fat intake on a ketogenic diet is often higher than on low-fat diets, but that the relationship between dietary saturated fat and cardiovascular disease is more complex than older guidelines suggested. It recommended that individuals on ketogenic diets have their cardiovascular risk profile monitored rather than assuming harm based on fat intake alone.

The Bottom Line

The 2024 Lancet review on low-carb diets presents a nuanced picture. Low-carbohydrate and ketogenic diets are effective for weight loss, glycaemic control in type 2 diabetes, and improvement in metabolic syndrome markers. The evidence is robust in these areas. For cardiovascular health, the picture is more complex: LDL cholesterol may rise, but triglycerides fall, HDL rises, and blood pressure often improves. Long-term weight loss is modest and comparable to other diets, but adherence may be easier because appetite is suppressed. Safety data are reassuring for metabolically healthy individuals and those with type 2 diabetes, though certain populations (pregnancy, type 1 diabetes, eating disorder history) require specialist guidance.

The review does not present ketogenic diets as a miracle or a universal solution. It presents them as a legitimate dietary approach with specific evidence-based benefits for specific populations. Whether a ketogenic diet is right for you depends on your metabolic health, your goals, your food preferences, and your ability to sustain it. If you’d rather not do the macro maths yourself, automatic macro tracking through the Keto Dieting app does it for you on Google Play and the App Store.

References

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2. Sumithran P, Prendergast LA, Delbridge E, et al. (2013). Ketosis and appetite-mediating nutrients and hormones after weight loss. European Journal of Clinical Nutrition. https://doi.org/10.1038/ejcn.2013.90
3. Westman EC, Yancy WS, Mavropoulos JC, Marquart M, McDuffie JR (2008). The effect of a low-carbohydrate, ketogenic diet versus a low-glycaemic index diet on glycaemic control in type 2 diabetes mellitus. Nutrition & Metabolism. https://doi.org/10.1186/1743-7075-5-36
4. Hallberg SJ, McKenzie AL, Williams PT, et al. (2018). Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at 1 Year: An Open-Label, Non-Randomized, Controlled Study. Diabetes Therapy. https://doi.org/10.1007/s13300-018-0373-9
5. Kosinski C, Jornayvaz FR (2017). Effects of Ketogenic Diets on Cardiovascular Risk Factors: Evidence from Animal and Human Studies. Nutrients. https://doi.org/10.3390/nu9050517
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7. Mavropoulos JC, Yancy WS, Hepburn J, Westman EC (2005). The effects of a low-carbohydrate, ketogenic diet on the polycystic ovary syndrome: a pilot study. Nutrition & Metabolism. https://doi.org/10.1186/1743-7075-2-35
8. Mardinoglu A, Wu H, Bjornson E, et al. (2018). An Integrated Understanding of the Rapid Metabolic Benefits of a Carbohydrate-Restricted Diet on Hepatic Steatosis in Humans. Cell Metabolism. https://doi.org/10.1016/j.cmet.2018.01.005
9. Hyde PN, Sapper TN, Crabtree CD, et al. (2019). Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss. JCI Insight. https://doi.org/10.1172/jci.insight.128308