Low-carb, keto, ketogenic nutrition and carb restriction — understand the science, mechanisms and clinical evidence behind each, all contextualised for South African foods and reviewed by registered dietitians.
Click any section below to expand the full content, including mechanisms, clinical evidence and cited sources.
A low-carbohydrate diet restricts dietary carbohydrates — sugars, starches and grains — in favour of protein and fat. The rationale is biological: carbohydrates are the primary driver of insulin secretion, and chronically elevated insulin promotes fat storage and metabolic dysfunction. By reducing carbohydrate intake, the body shifts from burning glucose to burning fat for fuel, a metabolic state called ketosis (at very low carb intakes) or simply a state of reduced insulin output (at moderate carb restriction).
Low-carb eating exists on a spectrum. A moderate low-carb diet might allow 50-130g of carbs per day, while a strict ketogenic diet restricts to 20-50g. The approach gained prominence in South Africa through the Banting movement, popularised by Professor Tim Noakes and The Real Meal Revolution. While evidence supports short-term benefits for weight loss, blood sugar control and triglyceride reduction, long-term safety data is more nuanced — and not all low-carb approaches are equal.
The quality of a low-carb diet matters enormously. A diet of processed meats, seed oils and minimal vegetables is low-carb but nutritionally poor. The healthiest low-carb approaches emphasise whole foods: non-starchy vegetables, healthy fats (olive oil, avocado, nuts), quality protein and minimal processed foods.
1Ludwig DS, Ebbeling CB. The carbohydrate-insulin model of obesity: beyond calories in, calories out. JAMA Intern Med. 2018;178(8):1098-1103.
2Noakes TD. Food addiction: the disease of the twenty-first century? S Afr J Clin Nutr. 2014;27(2):58-60.
3Hall KD, Bemis T, Brychta R, et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab. 2015;22(3):427-436.
A low-carb diet in its moderate form typically restricts carbohydrate intake to 50-130g per day — enough to meaningfully reduce insulin output and often improve blood sugar and triglycerides, but not so low as to induce ketosis. This makes it the most flexible and sustainable form of carb restriction for many people. It typically allows some fruit, small amounts of starchy vegetables, and even modest portions of whole grains, while eliminating refined sugars, processed carbs and most starches.
Sugar, sweets, sugary drinks, white flour, bread, pasta, rice, pastries, most cereals, starchy vegetables (potatoes in large amounts), beer.
What the Evidence Shows
Weight loss: A 2018 meta-analysis of 32 RCTs by Korsmo-Haugen et al. found low-carb diets produced greater short-term weight loss (3-6 months) than low-fat diets, though differences narrowed by 12 months. The advantage appears driven largely by spontaneous appetite reduction rather than metabolic advantage.
Blood sugar: Low-carb diets consistently reduce HbA1c and fasting glucose in type 2 diabetes. A 2021 systematic review by Goldenberg et al. found significant HbA1c reductions and often allowed reduction or cessation of diabetes medication — under medical supervision.
Lipids: Triglycerides typically drop significantly; HDL often increases. LDL may rise in some individuals — the significance of this on a low-carb diet is debated.
Who benefits most
Moderate low-carb diets show the strongest evidence for people with type 2 diabetes, insulin resistance, metabolic syndrome, and those who struggle with hunger on calorie-restricted low-fat diets. The appetite-suppressing effect of higher protein and fat can make adherence easier for many.
1Korsmo-Haugen HW, Brurberg M, Frafjord J, et al. Low-carbohydrate diets for overweight and obesity: a systematic review and meta-analysis. Obes Rev. 2018;19(11):1546-1559.
2Goldenberg JZ, Day A, Brinkworth GD, et al. Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission. BMJ. 2021;372:m4743.
3Mansoor N, Vinknes KJ, Veierød MB, Retterstøl K. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr. 2016;115(3):466-479.
The ketogenic (keto) diet restricts carbohydrates to approximately 20-50g per day — low enough to shift the body into nutritional ketosis, a metabolic state where the liver converts fat into ketone bodies (beta-hydroxybutyrate, acetoacetate, acetone) to fuel the brain and body. Protein is kept moderate (to avoid excessive gluconeogenesis) and fat provides the majority of calories. Originally developed in the 1920s as a treatment for drug-resistant epilepsy in children, the keto diet has become one of the most studied and debated dietary approaches of the modern era.
Macronutrient Ratios
Fat70-80% of total calories
Protein15-25% of total calories
Carbs5-10% of total calories (20-50g/day)
What Ketosis Means
In ketosis, blood ketones rise to 0.5-3.0 mmol/L. The brain, which normally relies on glucose, adapts to using ketones for approximately 70% of its energy needs. Ketones can be measured with blood ketone meters (most accurate), breath analysers, or urine strips (least reliable). It typically takes 2-7 days of strict carb restriction to enter ketosis, and a single high-carb meal can exit it.
Evidence: Benefits
Epilepsy: The strongest evidence base. A 2020 Cochrane review found ketogenic diets reduce seizures in children with drug-resistant epilepsy, with up to 50% achieving seizure freedom.
Weight loss: Multiple RCTs show keto produces rapid short-term weight loss, often 2-3x faster than low-fat in the first 3-6 months, largely through appetite suppression and water loss (glycogen depletion). Long-term results converge with other diets.
Type 2 diabetes: Hallberg et al. (2018) showed 60% of patients reversed T2D (HbA1c below 6.5% without medication) at 1 year on a continuous care intervention with ketogenic nutrition.
PCOS: Small studies suggest keto improves insulin sensitivity, androgen levels and menstrual regularity in PCOS.
The keto flu and adaptation
In the first 1-2 weeks, many experience headaches, fatigue, irritability, muscle cramps and constipation — known as the keto flu. This is primarily an electrolyte issue: as insulin drops, the kidneys excrete sodium, potassium and magnesium. Mitigate by increasing salt intake, staying hydrated, and supplementing electrolytes. Symptoms usually resolve within 2 weeks as the body adapts to ketones.
1Martin K, Jackson CF, Levy RG, Cooper PN. Ketogenic diet and other dietary treatments for epilepsy. Cochrane Database Syst Rev. 2020;(7):CD001033.
2Hallberg SJ, McKenzie AL, Williams PT, et al. Effectiveness and safety of a novel care model for the management of type 2 diabetes. Nutr Metab (Lond). 2018;15:10.
3Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013;67(8):789-796.
4Castellana M, Conte E, Giannini C, et al. Efficacy and safety of very low calorie ketogenic diet (VLCKD) in patients with overweight and obesity. Endocrine. 2020;68(2):275-286.
Ketogenic nutrition refers to the clinical and therapeutic use of ketosis — distinct from the keto diet for weight loss trend. It encompasses modified ketogenic diets used in neurology, very-low-calorie ketogenic diets (VLCKD) for obesity management under medical supervision, and emerging research into ketosis for metabolic disease, cognitive health and even cancer adjunct therapy. The distinction matters: therapeutic ketogenic nutrition is typically medically supervised, protein-controlled, and tailored to specific conditions — not a self-directed weight-loss diet.
Clinical Applications
Drug-Resistant Epilepsy
The classic 4:1 ketogenic diet (4g fat per 1g protein+carb) has been used since 1921. A 2020 Cochrane review confirms efficacy in children, with approximately 50% achieving greater than 50% seizure reduction and 10-15% becoming seizure-free. Modified Atkins and MCT diets offer more flexible alternatives.
Type 2 Diabetes Reversal
The Virta Health continuous care model (Hallberg et al. 2018) demonstrated that medically supervised ketogenic nutrition can reverse T2D in 60% of patients at 1 year, with improvements maintained at 2 years. Medication reduction is essential — insulin and sulfonylureas must be proactively reduced to avoid hypoglycaemia.
Cognitive and Neurodegenerative Disease
Ketones provide an alternative brain fuel that bypasses impaired glucose metabolism — relevant in Alzheimer’s, where brain glucose uptake is reduced. Small trials and observational data are promising but not yet definitive. The MCT-oil ketogenic approach is being studied for mild cognitive impairment.
Metabolic Syndrome and NAFLD
Ketogenic nutrition significantly reduces liver fat, improves insulin sensitivity and lowers triglycerides in non-alcoholic fatty liver disease (NAFLD), which affects up to 30% of South Africans.
Cancer Adjunct Therapy
The Warburg effect — many cancer cells rely on glucose — has prompted research into ketogenic diets as an adjunct to conventional therapy. Evidence is preliminary; human trials are ongoing. Ketogenic nutrition is NOT a standalone cancer treatment and should never replace evidence-based oncology care.
Therapeutic ketosis requires medical supervision
When used for clinical conditions — especially alongside medication — ketogenic nutrition must be supervised by a physician and dietitian. Diabetic patients on insulin or sulfonylureas risk dangerous hypoglycaemia without medication adjustment. Those with kidney disease, liver disease, or rare metabolic disorders (beta-oxidation defects) should not undertake ketogenic diets.
1Martin K, Jackson CF, Levy RG, Cooper PN. Ketogenic diet and other dietary treatments for epilepsy. Cochrane Database Syst Rev. 2020;(7):CD001033.
2Hallberg SJ, McKenzie AL, Williams PT, et al. Effectiveness and safety of a novel care model for the management of type 2 diabetes. Nutr Metab (Lond). 2018;15:10.
3Henderson ST. Ketone bodies as a therapeutic for Alzheimer's disease. Neurotherapeutics. 2008;5(3):470-480.
4Veldhorst MA, Westerterp-Plantenga MS, Westerterp KR. Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet. Am J Clin Nutr. 2009;90(3):519-526.
5Weber DD, Aminzadeh-Gohari S, Tulipan J, et al. Ketogenic diet in cancer therapy. Aging (Albany NY). 2018;10(10):2572-2583.
Carbohydrate restriction works through several interconnected mechanisms. Understanding them helps separate evidence from hype — and explains why low-carb approaches help some people more than others. The most rigorous evidence comes from controlled feeding studies and meta-analyses of randomised controlled trials.
Key Mechanisms
1. Insulin reduction: Carbohydrates are the primary insulin secretagogue. Reducing carbs lowers both fasting and postprandial insulin, which de-inhibits lipolysis (fat breakdown) and reduces fat storage signalling.
2. Appetite suppression: Higher protein and fat intake, along with ketones themselves, appear to increase satiety. Multiple studies show low-carb dieters spontaneously eat fewer calories — 200-500 kcal/day less — without conscious calorie counting.
3. Glycogen depletion and water loss: Each gram of glycogen stores 3-4g of water. Initial rapid weight loss on low-carb (2-4kg in week 1) is largely water, not fat. Fat loss follows more gradually.
4. Gluconeogenesis: When dietary carbs are scarce, the liver produces glucose from protein and glycerol. This is energy-expensive — the thermic effect contributes modestly to increased expenditure.
5. Triglyceride reduction: Lower carbohydrate intake reduces hepatic VLDL production, which lowers circulating triglycerides and often raises HDL.
What the Randomised Trials Show
Short-term (3-6 months): Low-carb diets typically produce 1-3kg greater weight loss than low-fat diets. A 2014 meta-analysis by Johnston et al. found significant short-term advantages.
Long-term (12-24 months): Differences narrow substantially. A landmark 2018 DIETFITS trial by Gardner et al. (609 participants, 12 months) found no significant difference in weight loss between healthy low-carb and healthy low-fat diets — genotype and insulin secretion did not predict response. Adherence mattered more than macronutrient ratio.
Metabolic health: Low-carb diets consistently outperform low-fat for triglycerides, HDL and HbA1c, even when weight loss is similar. LDL responses are variable — some rise, some fall.
The adherence factor
The DIETFITS trial and others confirm that long-term success depends on adherence, not on the specific macronutrient ratio. The best diet is one you can sustain. For some, low-carb is easier (less hunger); for others, a Mediterranean or plant-forward approach is more sustainable. Neither is universally superior.
1Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults. JAMA. 2018;319(7):667-679.
2Johnston BC, Kanters S, Bandayrel K, et al. Comparison of weight loss among named diet programs in overweight and obese adults. JAMA. 2014;312(9):923-933.
3Ebbeling CB, Feldman HA, Klein GL, et al. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance. BMJ. 2018;363:k2383.
4Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009;360(9):859-873.
Feature
Low-Carb
Keto
Keto Nutrition
Carb Restriction
Carbs/day
50-130g
20-50g
20-50g
Variable
Ketosis?
Usually no
Yes
Yes (therapeutic)
Depends
Flexibility
High
Low
Low (medical)
Variable
Protein
Moderate
Moderate
Controlled
Moderate
Fat %
40-50%
70-80%
75-85%
Variable
Best for
General weight/T2D
Rapid loss/T2D
Epilepsy/clinical
Metabolic health
Supervision
Self-directed ok
Self-directed*
Medical req.
Self-directed
Sustainability
Good
Challenging
Long-term protocols
Good
*Keto for T2D/medication users requires medical supervision.
Cardiovascular Risk
Low-carb diets improve several CVD markers: triglycerides drop (often 20-40%), HDL increases, and blood pressure often improves. However, the LDL response is variable — some individuals see significant LDL increases. A 2020 meta-analysis by Naseer et al. found no clear cardiovascular harm but called for longer-term data. The type of fat matters: replacing carbs with unsaturated fats (olive oil, nuts, avocado) is preferable to replacing with processed meats and saturated fats.
Type 2 Diabetes
This is the strongest evidence area. The 2021 BMJ systematic review by Goldenberg et al. found that low and very-low-carb diets achieved T2D remission (HbA1c below 6.5% without medication) in up to 50-60% of patients at 3-6 months, with substantial medication reduction. The Virta Health data showed 60% reversal at 1 year and 53% at 2 years. Crucially, these outcomes require medical supervision for medication management.
Weight Loss
Short-term weight loss on low-carb is consistently greater (1-3kg advantage at 3-6 months). Long-term, the advantage diminishes — adherence becomes the dominant factor. Ketogenic diets produce more rapid initial loss (largely water) but fat-loss rates converge with other approaches when calories are matched.
Long-Term Safety Concerns
The PURE study (Dehghan et al. 2017, 135,000+ participants) found very high carbohydrate intake (77%+ of calories) was associated with higher mortality, but also that very high fat (including saturated) was not associated with CVD. Seidelmann et al. (2018, 25,000+ participants, Lancet) found both very low and very high carbohydrate diets associated with higher mortality — with the lowest risk at 50-55% carbohydrate. Critics note these observational studies rely on food frequency questionnaires and may not reflect well-formulated low-carb diets. The totality of evidence suggests moderate carb reduction is safe; extreme restriction long-term needs more data.
1Goldenberg JZ, Day A, Brinkworth GD, et al. Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission. BMJ. 2021;372:m4743.
2Naseer F, Rizvi F, Hussain Z, et al. Low carbohydrate diets and cardiovascular risk factors: a meta-analysis. Cureus. 2020;12(9):e10588.
3Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality. Lancet Public Health. 2018;3(9):e419-e428.
4Dehghan M, Mente A, Zhang X, et al. Associations of fats and carbohydrate intake with cardiovascular disease and mortality. Lancet. 2017;390(10107):2050-2062.
South Africa has been at the global centre of the low-carb conversation, largely through the work of Professor Tim Noakes and the Banting movement. Banting — named after 19th-century undertaker William Banting — was re-popularised in SA through The Real Meal Revolution (2013) and the Noakes Foundation’s Eat Better South Africa programme. The approach advocates whole-food, low-carbohydrate, moderate-protein, higher-fat eating, with an emphasis on South African ingredients.
SA Low-Carb Friendly Foods
Ostrich meat — lean, high-protein, proudly South African
Boerewors (low-carb) — check for filler-free varieties
Biltong and droëwors — excellent low-carb snacks (check for sugar)
Fish — snoek, hake, kingklip, yellowtail
Avocados — SA-grown, excellent fat source
Macadamia nuts — grown in Limpopo and KZN
Leafy greens — spinach, cabbage, morogo
Eggs and full-fat dairy — versatile and affordable
Adapting SA staples
Traditional South African meals are carb-heavy — pap, rice, bread, samp. Low-carb adaptations include cauliflower rice instead of rice, pap made from cauliflower or ground flaxseed, sweet potato in moderation (lower-carb than regular potato), and extra vegetables replacing starch on the plate. Braais are naturally low-carb-friendly — focus on the meat, fish and salads, skip the bread rolls and potato salad.
1Noakes TD. Food addiction: the disease of the twenty-first century? S Afr J Clin Nutr. 2014;27(2):58-60.
2Noakes TD, Creed KE. The Eat Better South Africa programme. S Afr J Clin Nutr. 2016.
Common Side Effects
Initial adaptation (keto flu): headaches, fatigue, dizziness, muscle cramps, constipation — usually resolves in 1-2 weeks with electrolyte management. Longer-term: some report reduced exercise performance during high-intensity work (though endurance may improve). Constipation is common if vegetable/fibre intake is inadequate. Keto breath (acetone smell) occurs during ketosis.
Who Needs Medical Supervision
Type 1 diabetes: Ketogenic diets carry a risk of diabetic ketoacidosis (DKA) — a life-threatening condition distinct from nutritional ketosis. Any T1D attempting low-carb must do so with endocrinologist supervision and adjusted insulin protocols. Type 2 diabetes on insulin or sulfonylureas: These medications can cause hypoglycaemia on a low-carb diet. Medication must be proactively reduced by a physician. Kidney disease: Higher protein intake may stress compromised kidneys. Low-carb can be adapted but needs nephrology input. Pregnancy and breastfeeding: Strict keto is not recommended. Moderate low-carb with adequate nutrients may be appropriate with professional guidance. Rare metabolic disorders: Beta-oxidation defects, porphyria — ketogenic diets are contraindicated.
Common Pitfalls
• Eating too much processed meat and not enough vegetables
• Neglecting electrolytes (sodium, potassium, magnesium) during adaptation
• Treating keto as permission to eat unlimited calories — fat has 9 kcal/g
• Quitting too early during the 1-2 week adaptation phase
• Not getting enough fibre from non-starchy vegetables
• Ignoring food quality — low-carb junk food is still junk food
Athletes
Low-carb may impair high-intensity (glycolytic) performance — sprinting, weightlifting, HIIT. Endurance athletes often adapt well and may benefit from fat adaptation. The train-low, race-high strategy (low-carb training, carb-loading for events) is being studied. SA athletes should experiment during off-season.
When to see a professional
If you have diabetes (type 1 or 2), kidney or liver disease, are pregnant, take medications that affect blood sugar or blood pressure, or are unsure which approach suits you — consult an HPCSA-registered dietitian and your GP before starting. Blood tests (lipid panel, HbA1c, kidney function) at baseline and 3-6 months are strongly recommended.
1Kosinski C, Jornayvaz FR. Effects of ketogenic diets on cardiovascular risk factors. Nutrients. 2017;9(5):495.
2Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013;67(8):789-796.
3Burke LM. Re-examining high-fat diets for sports performance: did we call the nail in the coffin too soon? Sports Med. 2015;45(S1):S33-S49.
Whether you're managing diabetes, seeking weight loss or exploring therapeutic ketosis — connect with HPCSA-registered professionals across South Africa who can guide you safely, adjust medication and monitor your progress.
Low-carbohydrate eating has been one of the most significant dietary movements in South Africa, driven by Professor Tim Noakes and the Banting revolution. But behind the cultural phenomenon lies a substantial and growing body of scientific evidence — from randomised controlled trials showing short-term weight loss advantages to landmark studies demonstrating type 2 diabetes remission through ketogenic nutrition. HealthLab’s Low-Carb Diets guide brings together peer-reviewed evidence, cited sources and South African-contextualised advice to help you navigate the spectrum of carbohydrate restriction. Whether you’re considering a moderate low-carb approach, a strict ketogenic diet for metabolic health, or therapeutic ketogenic nutrition for a clinical condition, our evidence-based content — reviewed by HPCSA-registered dietitians — provides the honest, balanced information you need to make safe and informed choices.
