saudigastro.com/patients/weight-loss-diets-evidence
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Common
Red flags
5
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
What is it?
A weight-loss diet is an eating pattern that lowers energy (calorie) intake below what the body uses, so it draws on stored fat. The main types studied are: calorie-restricted balanced diets (including low-fat), low-carbohydrate diets (including ketogenic, usually under 50 g of carbohydrate a day), the Mediterranean diet (vegetables, fruit, legumes, whole grains, olive oil, fish, little red meat), and meal-replacement or total-diet-replacement programmes (shakes or soups replacing some or all meals, about 800 to 1,000 kcal a day in the medical programmes). Intermittent fasting is covered in a separate article.
How common is it?
Trying to lose weight is very common: a large share of adults with overweight or obesity try to lose weight each year. Only a minority keep the weight off long-term without continuing support, which is why the evidence on maintenance matters as much as the evidence on loss.
Why does it happen?
People look for a diet because weight affects health and daily life. But the body defends its weight: after weight loss, hunger hormones rise and energy use falls, so regain is common. This is biology, not weakness. Fad diets promise rapid results, but quick loss is largely water and muscle and is usually regained. Some people also turn to unsafe methods (extreme restriction, laxatives, diuretics, unregulated slimming products), which can harm the liver, heart and mind.
Symptoms
- Wanting to lose weight for health, fitness or appearance
- Repeated cycles of losing and regaining weight
- Hunger, tiredness, irritability or dizziness on very low-calorie diets
- Constipation, bad breath, headaches or cramps, especially in the first weeks of low-carbohydrate diets
- Preoccupation with food, guilt about eating, or binge eating
Red flags — seek urgent medical care
Fainting, palpitations, chest pain or severe weakness on a diet
May be salt or potassium imbalance, low blood pressure or heart rhythm problems. Stop the diet and go to the emergency room.
Severe right upper belly pain, especially after fatty meals, vomiting, or yellow skin during rapid weight loss
Rapid weight loss can cause gallstones and gallbladder or pancreas inflammation. Seek urgent care.
Diabetes with insulin or glucose-lowering tablets: shakiness, sweating, confusion or low sugar readings during dieting
Low blood sugar (hypoglycaemia) can be dangerous; treat it and call your doctor, who must adjust your medicines before or during any diet.
Binge eating, purging, laxative or diuretic misuse, or fear of gaining weight with very restricted eating
Possible eating disorder. These are treatable; see your doctor or a mental health professional soon, and urgently if you feel faint or unsafe.
Unplanned weight loss, black stools or blood in the stool, or persistent vomiting
Not related to a diet. Needs urgent medical review.
How is it diagnosed?
No test is needed to choose a diet, but a health check before you start is wise if you have diabetes, heart, kidney or liver disease, are pregnant or breastfeeding, take regular medicines or are over 65. A clinician or dietitian can assess your weight, waist, blood pressure, blood sugar, cholesterol and liver tests, review medicines that cause weight gain or may need adjustment when you eat less, and screen for eating disorders and depression. They will also agree a realistic goal with you.
What the latest science says
Large trials and meta-analyses show: (1) Diet type matters less than adherence. In the DIETFITS randomised trial (JAMA 2018) healthy low-fat and healthy low-carbohydrate diets gave similar average loss at 12 months (about 5 to 6 kg), with large individual differences in both groups; a meta-analysis (JAMA 2014) found differences between named diets of only 1 to 2 kg or so. (2) Low-carbohydrate and Mediterranean patterns often do slightly better than low-fat for blood sugar and triglycerides, and the PREDIMED trial (2018) showed the Mediterranean diet with olive oil or nuts lowers heart disease, even though weight loss was small. (3) Structured meal-replacement programmes work best for early, larger loss: in the DiRECT trial (Lancet 2018 and 2019), a low-calorie total diet replacement for 3 to 5 months, followed by structured food reintroduction and support, led to type 2 diabetes remission in nearly half of participants at 1 year and about a third at 2 years in primary care, with an average loss of about 10 kg at one year. (4) Typical loss with intensive lifestyle programmes is about 5 to 10% of body weight in 6 to 12 months; in the Look AHEAD trial about 6% was still lost after 8 years in the intervention group, and weight regain is the rule without ongoing support. (5) Weight loss of 5 to 10% improves blood pressure, glucose and liver fat; 10% or more is linked to MASLD improvement. (6) Very rapid loss raises gallstone risk. Evidence for sustained benefit of “detox”, juice-only and extreme-restriction plans is lacking. Ketogenic diets can be tried under supervision, but long-term evidence is limited and they may raise LDL cholesterol in some people. Guidance from the American Diabetes Association (2025), NICE (2025), Obesity Canada (2022) and the European Association for the Study of Obesity supports individualised plans, behavioural support and long-term follow-up.
Outlook — what to expect
With a realistic plan, most people can lose a meaningful amount of weight (5 to 10%) and improve their health. Maintaining it is the harder part: regular weighing, regular activity (around 200 to 300 minutes a week helps for maintenance), breakfast and home cooking, ongoing contact with a clinic or group, and sometimes medicines or surgery, all improve the odds. People who regain weight have not failed; the condition is chronic, and treatment may need to continue or be changed.
Treatment
Habits & Lifestyle
Behaviour support is a key part of every effective programme.
- Set realistic goals: 0.5 to 1 kg a week at most, or 5 to 10% of weight over about 6 months.
- Self-monitor: weigh weekly, note food in a diary or app, and record steps; people who self-monitor lose more.
- Be active: build to 150 minutes a week of moderate activity for health and more for maintenance, with strength training to protect muscle.
- Sleep well, plan meals, shop with a list, and keep tempting foods out of sight.
- Join a structured programme, group or clinic; support doubles the chance of success compared with going alone.
Diet
Pick an approach that suits your health, culture, budget and preferences. A dietitian can help you choose and adjust it.
- Calorie-controlled balanced diet: a deficit of about 500 to 750 kcal a day below your needs usually gives the steady loss described above. Keep protein adequate (eggs, fish, chicken, legumes, laban), fill half the plate with vegetables, and choose whole grains over refined ones.
- Mediterranean-style diet: a good all-round choice for heart and liver health, easily adapted to Saudi foods (fish, hummus, ful, lentils, salads, olive oil, nuts, yoghurt, fresh fruit, dates in small portions). Weight loss is usually modest unless calories are also reduced.
- Low-carbohydrate diet: may help with early weight loss, blood sugar and triglycerides. Choose vegetables, protein and unsaturated fats rather than processed meat and saturated fat. People with diabetes on medicines, with kidney disease or pancreatitis, or who are pregnant should do this only with medical supervision. Very-low-carbohydrate ketogenic diets can cause side effects such as constipation, headaches and raised LDL cholesterol.
- Low-fat diet: works equally well when it focuses on whole, minimally processed foods; avoid “low-fat” products loaded with sugar.
- Meal replacements and total-diet-replacement (about 800 to 1,000 kcal a day for 8 to 12 weeks, then step-wise food reintroduction): effective for larger early loss and for type 2 diabetes remission, but only under medical or dietitian supervision. Not suitable in pregnancy, type 1 diabetes, kidney disease, liver disease, a history of eating disorders, or for people on certain medicines.
- Ultra-processed foods, sugary drinks and large portions add calories without filling you; reducing them helps with any plan.
- Maintenance: after loss, move gradually to a sustainable pattern you enjoy, keep weighing, keep active, and return to your plan early if weight rises a few kilos.
- Be wary of: detox teas, “fat burner” capsules, herbal slimming mixes, injectable products from unlicensed sellers, and extreme plans promising more than 1 kg a week. Several have been linked to liver injury and heart problems.
Medications
Medicines may be added to a diet plan for people who qualify. Do not start or stop prescription medicines on your own when changing your diet.
- Diabetes medicines (insulin, sulfonylureas) and blood-pressure medicines often need adjusting when you eat less or lose weight; tell your doctor before you start.
- Prescription anti-obesity medicines, including GLP-1-based treatments, are options for eligible adults alongside diet and activity; see the GLP-1 article.
- Vitamin and mineral supplements are generally not needed on a balanced diet but may be advised on very-low-calorie plans or after bariatric surgery.
- Avoid non-prescribed “slimming” products.
Procedures & Surgery
Surgery and endoscopic procedures are for people for whom diet and medicines are not enough.
- Metabolic-bariatric surgery is the most effective long-term treatment for severe obesity and obesity with serious complications; see our bariatric surgery article.
- Endoscopic balloons or sleeve procedures are options in some centres.
- A pre-programme medical check (blood tests, liver ultrasound, and a gallstone check if indicated) may be advised.
Living with the condition
- Judge success by health (energy, blood tests, fitness) and not only by weight.
- Avoid “all or nothing” thinking; one big meal does not undo your progress.
- Plan for events (weddings, Eid, Ramadan gatherings) with smaller portions and fewer sweets, without guilt.
- Seek help early for emotional eating or an eating disorder.
In the Saudi context
Hospitality foods such as large rice-and-meat dishes, sweets, dates and sweet tea or Arabic coffee with sugar can add many calories. Adapting rather than abandoning traditional food works best: smaller portions of rice (or brown rice), more salad and vegetables, grilled fish or chicken, ful and lentils, laban without sugar, and fruit as dessert; dates are nutritious but calorie-dense, so count two or three as a portion. Check labels on locally sold diet products and use only SFDA-registered items. Online and social-media “diet” offers are often unregulated. Many hospitals and primary care centres have clinical dietitians; ask for a referral.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Which diet is safest and most realistic for me given my health conditions?
- Do my medicines (diabetes, blood pressure) need to be changed if I diet?
- How much weight should I aim to lose, and how fast?
- Would a meal-replacement programme, medicine or surgery be appropriate for me?
- How can I keep the weight off, and who can support me?
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Status: Approved for publication by SGA; individual clinician review is ongoing · Published 24/04/2026
For general education only; it does not replace your doctor’s advice. Individual clinician review of this guide is ongoing. SGA clinician? Review this guide