Low-carbohydrate diets are commonly discussed in relation to weight management and type 2 diabetes. Interest in these approaches has increased in both research and clinical practice in recent years.
These diets vary considerably in how they are implemented, and findings across studies are mixed and sometimes inconsistent. While some research suggests potential benefits, questions remain about long-term outcomes and overall diet quality.
Understanding what is supported by evidence, and how these diets can be implemented healthfully is important for both individuals and healthcare professionals.
What Is a Low-Carbohydrate Diet?
There is no single definition. In general, low-carbohydrate diets reduce carbohydrate intake relative to typical dietary patterns. Carbohydrates are found in foods such as grains, fruits, vegetables, legumes and sugary foods.
Some approaches involve moderate restriction, while others reduce carbohydrate intake more substantially. Very low-carbohydrate or ketogenic diets typically limit carbohydrate to below 50 g per day, whereas more moderate approaches allow higher intakes (1).
However, carbohydrate quantity alone does not determine health effects. The foods used to replace carbohydrates and overall dietary quality are likely to play an important role.
What Counts as a Low-Carbohydrate Diet?
| Dietary Pattern | Approximate Carbohydrate Intake | % of Total Energy | Typical Description |
| Higher carbohydrate / typical diet | 225–325 g per day | 45–65% | Reflects standard guidelines |
| Moderate-carbohydrate diet | 130–225 g per day | 26–45% | Slight reduction |
| Low-carbohydrate diet | 50–130 g per day | 10–25% | Noticeable restriction |
| Very low carbohydrate / ketogenic | <50 g per day | <10% | Often aims for ketosis |
Values are approximate and depend on total energy intake. Definitions vary across studies and clinical guidelines.
How Might Low-Carbohydrate Diets Work?
Low-carbohydrate diets may influence weight and metabolic health through several mechanisms.
Smaller rises in blood glucose
Carbohydrates are the main nutrient that raises blood glucose after meals. Reducing carbohydrate intake can lead to smaller post-meal glucose increases, which may improve glycaemic control and reduce insulin demand in type 2 diabetes (2)(3).
Higher protein intake and satiety
Many low-carbohydrate diets increase protein intake. Protein is generally more filling than carbohydrate or fat and may help reduce overall calorie intake (4).
Ketosis in very low-carbohydrate diets
Very low-carbohydrate diets may induce nutritional ketosis, where the body produces ketones from fat. Some research suggests ketosis may influence appetite, although findings are mixed (5).
Early water and glycogen loss
Initial weight loss often reflects depletion of stored carbohydrate (glycogen) and associated water loss, contributing to greater short-term reductions (1).
Reduced intake of refined carbohydrates
Benefits may also arise from reducing sugary drinks, sweets, and refined grains, and replacing them with minimally processed foods (1).
Glycaemic Control and Type 2 Diabetes
Reducing carbohydrate intake can lead to smaller rises in blood glucose after meals. Some studies report reductions in HbA1c and, in certain cases, reductions in medication requirements (3), (6).
A narrative review by Adrian Brown and colleagues suggests that low-carbohydrate diets, when appropriately supported, can be considered safe for individuals who find them acceptable and sustainable. This indicates that carbohydrate restriction may represent one of several viable options for managing glycaemia (2).
Weight Management
Low-carbohydrate diets are often associated with greater short-term weight loss compared with higher-carbohydrate diets. However, differences tend to diminish over time (8),(4).
The DIETFITS trial compared a healthy low-fat diet with a healthy low-carbohydrate diet over 12 months and found no meaningful difference in weight loss between groups. Participants in both groups were encouraged to focus on minimally processed foods, suggesting adherence and diet quality are key determinants of success (8).
Lipid Markers
Low-carbohydrate diets are often associated with reductions in triglycerides and increases in HDL cholesterol. However, responses in LDL cholesterol are variable. Some individuals experience increases, particularly when diets are high in saturated fat (9).
Appetite and Adherence
Very low-carbohydrate diets may influence appetite through ketosis and higher protein intake. Some individuals report improved satiety, although findings are inconsistent (5).
If a dietary pattern is easier to follow, adherence may improve, likely influencing long-term outcomes.
Comparison With Other Dietary Approaches
Low-carbohydrate diets are one of several dietary approaches that may support metabolic health. Mediterranean-style, higher-protein and lower-fat diets have also demonstrated benefits.
Comparative trials generally show modest differences in weight loss between approaches when calorie intake and support are similar. Mediterranean-style diets have strong evidence for cardiovascular risk reduction, suggesting that multiple dietary patterns can be effective (8).
Diet Quality
Carbohydrate restriction alone does not determine whether a diet is healthful. Two individuals consuming similar amounts of carbohydrate may have very different dietary patterns.
Healthful low-carbohydrate diets typically emphasise vegetables, minimally processed foods, and varied protein sources. Unsaturated fats from olive oil, nuts, seeds, and oily fish can replace carbohydrates while maintaining cardiovascular health. Less balanced approaches may rely heavily on processed meats, butter, and highly processed “low-carbohydrate” products. These patterns may be lower in fibre and higher in saturated fat, which may influence cardiovascular risk.
Individual Variation
Responses to low-carbohydrate diets vary. Some individuals find carbohydrate restriction helpful and sustainable, while others prefer more flexible approaches. Long-term adherence appears to be a key determinant of success.
Genetic differences have been proposed as a potential influence on dietary response. However, large trials have not found consistent evidence that genetic profiles meaningfully predict whether individuals respond better to low-carbohydrate or low-fat diets. This suggests that behavioural factors, such as adherence and food choices, remain more important in practice.
Potential Limitations and Risks
- Fibre intake may decrease if plant foods are limited
- LDL cholesterol may increase in some individuals
- Restrictive approaches may reduce micronutrient intake
- Very low-carbohydrate diets may be difficult to sustain
- Medication adjustment may be required in diabetes
- Temporary fatigue or headache may occur initially
These considerations highlight the importance of appropriate implementation and monitoring.
In Summary
Well supported
• May improve glycaemic control
• Greater short-term weight loss
• Triglycerides often decrease
Variable or uncertain
• LDL cholesterol responses differ
• Appetite effects inconsistent
• Long-term superiority not established
Important considerations
• Diet quality remains central
• Fibre intake should be maintained
• Sustainability and individual preference are key
Interpreting the Evidence
Low-carbohydrate diets represent one of several dietary approaches that may support weight management and metabolic health. Evidence suggests potential benefits, particularly for glycaemic control and short-term weight loss. However, these diets are not clearly superior to other approaches, and outcomes depend largely on adherence and overall dietary quality.
For individuals choosing to follow a low-carbohydrate diet, focusing on vegetables, minimally processed foods, and balanced fat sources may help support long-term health.
No single dietary approach is universally optimal, and supporting individuals in finding a sustainable, balanced way of eating remains central to long-term health.
References
1. Landry MJ, Crimarco A, Gardner CD. Benefits of Low Carbohydrate Diets: a Settled Question or Still Controversial? Curr Obes Rep. 2021 Sep 1;10(3):409. doi:10.1007/S13679-021-00451-Z PubMed PMID: 34297345.
2. Brown A, McArdle P, Taplin J, Unwin D, Unwin J, Deakin T, et al. Dietary strategies for remission of type 2 diabetes: A narrative review. Journal of Human Nutrition and Dietetics. 2022 Feb 1;35(1):165–78. doi:10.1111/JHN.12938;PAGE:STRING:ARTICLE/CHAPTER PubMed PMID: 34323335.
3. Snorgaard O, Poulsen GM, Andersen HK, Astrup A. Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes. BMJ Open Diabetes Res Care. 2017 Feb 1;5(1):e000354. doi:10.1136/BMJDRC-2016-000354 PubMed PMID: 28316796.
4. Bueno NB, De Melo ISV, De Oliveira SL, Da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. British Journal of Nutrition. 2013 Oct 14;110(7):1178–87. doi:10.1017/S0007114513000548 PubMed PMID: 23651522.
5. Gibson AA, Seimon R V., Lee CMY, Ayre J, Franklin J, Markovic TP, et al. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obes Rev. 2015 Jan 1;16(1):64–76. doi:10.1111/OBR.12230 PubMed PMID: 25402637.
6. Goldenberg JZ, Johnston BC. Low and very low carbohydrate diets for diabetes remission. The BMJ. 2021 May 24;373. doi:10.1136/bmj.n262 PubMed PMID: 33441384.
8. Gardner CD, Trepanowski JF, Gobbo LCD, Hauser ME, Rigdon J, Ioannidis JPA, et al. 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. 2018 Feb 20;319(7):667–79. doi:10.1001/JAMA.2018.0245 PubMed PMID: 29466592.
9. Kirkpatrick CF, Bolick JP, Kris-Etherton PM, Sikand G, Aspry KE, Soffer DE, et al. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the Nat…. J Clin Lipidol. 2019 Sep 1;13(5):689-711.e1. doi:10.1016/j.jacl.2019.08.003 PubMed PMID: 31611148.
