Ketogenic diets: Worth the carb cut?
Where keto meets real life (and real plates)
Ketogenic diets are a very low-carb way of eating, typically consisting of around 20–50 grams of carbohydrates per day, with moderate protein and high fat content. Our bodies normally use carbohydrates as a primary source of energy, so when you follow a ketogenic diet, the body shifts to using fats as a source of energy (more accurately, ketone bodies, which are derived from fat “burning”).
You may have heard variations of ketogenic diets: classic keto, the modified Atkins, and “Mediterranean‑like” styles that emphasise olive oil, fish, nuts and lots of non‑starchy vegetables. These choices affect how easily the diet can be followed.
So, what motivates people to try keto diets?
Common reasons may include trying to lose weight, improving appetite control, stabilising blood sugar levels and increasing focus. Food is social, after all. A plan should (ideally) work at a birthday, a holiday and on date night. Especially when you want to think about your company, not your macros.
What the science says
Keto first appeared in the clinical scene to treat certain types of epilepsy that did not respond to traditional medications. Since then, studies have investigated the effects of keto diets on weight, diabetes, cholesterol levels, brain function and exercise (among others).
- Weight: Weight loss may happen early on. But by about a year, the results tend to be similar to those of other calorie-restriction plans. Appetite control and structure may contribute to early success, but sustainability in the long run could be an issue.
- Type 2 diabetes: Short‑term improvements in long‑term blood sugar markers have been observed. However, if you take medication that lowers blood sugar, any change to your diet should be discussed with your diabetes team.
- Cholesterol: Triglyceride levels may drop, and “good” HDL cholesterol increases have been observed. “Bad” LDL cholesterol levels can increase in some individuals, particularly with higher intakes of saturated fats (e.g. butter, coconut oil and fatty cuts of meat). Discuss regular checks with your GP.
- Brain function: Early research suggests ketogenic approaches may support brain energy use and some cognitive measures in certain conditions, including Alzheimer’s disease, but findings are preliminary and mixed. The brain can use ketone bodies as an alternative fuel. Some otherwise healthy people report feeling more focused on a keto diet. This area is still under investigation.
- Exercise: The muscle-to-fat balance can improve, as indicated by small reductions in BMI. High‑intensity efforts may dip in the first weeks; steady cardio is usually less affected. Training quality and total energy are the most important factors.
How do carbs really fit into the picture?
After examining the scientific evidence, it is worthwhile to step back and reconsider the role of carbohydrates.
Carbohydrates are not necessarily only a source of energy. Vegetables, fruits, legumes, whole grains and starchy vegetables provide fibre and micronutrients that support heart and gut health.
Very low fibre intakes can cause constipation. Aiming for the UK's daily recommended 30g of fibre is a good starting point.
What a day on keto may look like as food
So if keto focuses mainly on fats, moderate protein intake and low carb intake, what would a typical “keto” day menu look like?
- Breakfast: an omelette with vegetables, cheese and mashed avocado plus a handful of berries on the side, accompanied by coffee or tea.
- Lunch: salmon or tofu on greens with olive oil, tahini and lemon and a handful of walnuts.
- Snack: Greek or soy yoghurt with chia seeds and cinnamon.
- Dinner: chicken or tempeh stir-fried with broccoli, courgette and pak choi, finished with sesame oil and sunflower seeds.
- Drinks: water, unsweetened tea/coffee.
Who should get medical advice first?
Pause and seek medical advice if you have pancreatitis, liver, gallbladder or kidney disease, type 1 diabetes, are pregnant or breastfeeding, have a history of eating disorders, or have high cholesterol levels running in your family.
If you use diabetes medication that lowers your blood sugar levels, adjustments should be made under medical supervision due to the risk of very low blood sugar levels (hypoglycaemia).
Things to keep in mind if you choose keto
- Success can mean more than just weight loss: it is also about maintaining steady energy levels, getting good sleep, supporting your mood and overall well-being.
- Build your plates around non-starchy vegetables, quality protein sources (such as fish, poultry, eggs, tofu, tempeh and yoghurt), and ideally, mostly unsaturated fats (olive oil, nuts, seeds and avocado).
- Maintain steady protein intake (1.0–1.5 g/kg/day). Keep carbs low or adjust them according to your training needs.
- If you live with diabetes or have concerns about cholesterol levels, consult with your healthcare team.
Wondering if keto fits your lifestyle and needs?
Low-carb may not suit everyone. Mediterranean-style, higher-protein, or low-GI eating can support weight and metabolic health with potentially fewer social and performance trade-offs. Lifters and runners often find moderate-carb plans (40-50% of total calories from carbs) improve training and long-term adherence. Choose what suits you best, and if in doubt, consult with a medical professional or a registered dietitian.
Sticking with your plan
Once an approach is chosen (keto, moderate-carb, or Mediterranean-like), success depends on what can be maintained, especially during busy periods. Many people adjust or discontinue their plan within 6–12 months, not necessarily due to a lack of willpower, but because routine, relationships and personal enjoyment play important roles.
What can help:
- Flex your rules, not your values: keep the core (protein, non-starchy vegetables, unsaturated fats). You could allow planned carb “windows” for specific events or training sessions.
- Plan for social food: scan menus for protein and veggie anchors. Add carbs if you feel like it, then move on without obsession.
- Routine beats perfection: repeatable breakfasts, batched lunches and easy-to-prepare dinners can help you get through busy weeks.
- Watch signals, not just scales: energy, mood, sleep, training and digestion and adjust accordingly. Listen to your body and your mind.
Common side effects and practical fixes
During the first week, some people may experience a slump or “keto flu” (including headache and fatigue), partly due to changes in fluid and salt levels. Prioritise fluids and include salty foods, as well as food sources of potassium (such as vegetables) and magnesium (leafy green vegetables, nuts and seeds).
Another potential side effect is constipation, as fibre intake goes down. Consider including plenty of non-starchy vegetables, seeds (such as flax and chia, in moderation) and maintaining adequate fluid intake.
Cramps and sleep changes may occur. Acetone, one type of ketone body, can affect breath odour (keto breath). If these symptoms persist, consult a medical professional.
If you develop persistent gut issues, dizziness or fainting, a marked rise in “bad” LDL cholesterol, cycles of restriction and bingeing, or low mood, stop and seek medical advice.
The bottom line
Keto diets can work for some people, often through appetite control and structure, but long-term success depends on enjoyment, social fit and your health (such as cholesterol levels, mood and energy levels). Professional support is advised to reduce potential risks.
If you are unsure, speak with your healthcare team or a registered dietitian to develop a personalised plan.
The best approach is one that you can live with on both busy and quiet days, being supportive of your health, training and overall life.
Spread the love with food.
Emiliano Pena is a dietician based in London
This article is for general information only and is not a substitute for personalised medical or nutritional advice.
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