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Rapid weight loss through calorie restriction and/or intermittent fasting are very effective ways to lose weight and reduce insulin resistance, however, these approaches are not suitable for everyone.
Whilst we always recommend talking to your usual health professional before starting any new diet or exercise regime, it is important to note that the 800 calories a day plans (The Very Fast 800 and The Fast 800 Keto) or intermittent fasting approaches (The New 5:2 and Transition 3:4 plans and TRE) are not suitable for the following people:
(a) People who are underweight and/or have an eating disorder, or a history or suspicion of an eating disorder.
(b) Children (under 18 years old).
(c) Type 1 diabetics.
(d) People who are pregnant, breastfeeding or undergoing fertility treatment.
(e) People who have a significant psychiatric disorder or substance abuse.
(f) People who are under active medical investigation or treatment, or have a significant medical condition affecting ability to comply with diet.
(g) People who have had a recent cardiac event, myocardial infarction or cerebrovascular accident (< 3 months previously) or other heart abnormalities.
(h) People who have had uncontrolled heart disease, uncontrolled hypertension, kidney failure or liver failure.
(i) People who are feeling unwell, have a fever, are frail or recovering from significant surgery (< 6 months ago).
(j) People who are on insulin. This is to avoid a potentially dangerous drop in blood sugar (hypo).
(k) People who are on ‘flozin’ medication (known as SGLT2 inhibitors, taken to reduce blood sugars, such as Dapagliflozin or Canagliflozin). This is to avoid the rare complication and potentially dangerous condition called euglycaemic diabetic ketoacidosis (DKA), where, despite having normal or only mildly raised blood glucose, the medication can mask a serious complication of diabetes requiring urgent attention.
(l) People taking sulphonylureas.
(m) People with a healthy BMI. The Very Fast 800 is only intended for those who are overweight or obese. If you’re looking to improve your healthy lifestyle, the benefits of a Mediterranean-style diet, exercise and mindfulness will significantly help. The New 5:2 and The Way of Life are more flexible, less restrictive approaches that still have impressive health benefits.
You must also discuss with a medical professional before starting the 800 calorie or intermittent fasting approaches if any of the following apply:
(a) You have a significant underlying medical condition.
(b) If you have type 2 diabetes and are on medication, it will be necessary to adjust your medication. It may need to be reduced or stopped as blood sugars improve and to avoid hypos.
(c) If you are on certain diabetic medication and have ‘hypoglycaemia unawareness’ (you cannot tell if you have a ‘hypo’ when your sugar level drops).
(d) If you are on blood pressure medication, this may need to be reduced or stopped as blood pressure improves.
(e) If you have a history of psychiatric conditions.
(f) If you are taking any other medications, e.g. blood thinners.
(g) If you have moderate or severe retinopathy, you will need extra screening within 6 months (as retinopathy can sometimes get worse when blood sugar improves).
(h) People with epilepsy (though there is some evidence that diet can improve epilepsy).
(i) If you do not have a gallbladder, have a history of gallstones, and/or currently have gallstones and are considering following The Fast 800 Keto meal plans – other dietary approaches on The Fast 800 Programme may be more appropriate, please discuss with your usual doctor before commencing.
Also, if you do have diabetes, you should check with your GP to confirm that you have type 2 diabetes, as there are other rarer forms of diabetes, such as pancreatic or monogenic diabetes, which will not respond in the same way to weight loss.