In Conversation with Doctors


Intermittent Fasting vs Keto Diet for weight loss

by Ms Rozanna M. Rosly, Clinical Dietitian and Dietetic Manager UMSC

Co-writers : Lim Xin Le, Nurul Farihah binti Mohd Yaakob, Chin Hui Voon


Intermittent Fasting Vs Keto Diet for Weight loss – is it sustainable & effective?

Discovering the effectiveness of the latest trends for weight loss, intermittent fasting and keto diet.

Do you know the basic principles of losing body fat and weight?

Excess body weight (overweight/obesity) is when one has excess fat stores in the body. Fat stores depend on the energy balance of our body. Therefore, to lose weight, one needs to achieve a negative energy balance . This means that we need to either burn more calories than what we have taken or to reduce our calorie intake to counter the low energy expenditure. The commercial weight loss programs and various diets attempt to achieve this for weight loss. But the main question is really – are you doing right? Which one is more effective? Is it sustainable for long term weight loss and maintenance? Is it safe with no side effects?

Discovering the facts about intermittent fasting and keto diet

Intermittent fasting and keto diet are two popular diet trends today. Do you know how they work in our body to achieve weight loss?

What is intermittent fasting?

Intermittent fasting is a concept where one alternates between eating and fasting and eating in specific time periods. It does not restrict what you’re eating, it just dictates a time period when you are able to eat

While there are several types of intermittent fasting (i.e. time-restricted eating, alternate-day fasting, religious fasting, etc.), the main principle is the same – to restrict food intake by focusing on the timing of when one can consume meals either within a day or a week[1]. The mechanism is simple – by cutting down the time availability to consume food, our body receives lesser calories, thus is forced to use the existing fat stores in our body as energy, leading to weight loss.




Can I eat anything whilst doing intermittent fasting?

There are no rules  as such regarding the type of food you should be eating when intermittent fasting however I would recommend getting advice and guidance  from  a qualified healthcare professional before starting to ensure you are  fasting safely and effectively and getting the most out of your diet whilst doing it. It is important to eat whole foods and still adhering to a healthy, balanced diet to ensure you are nourishing your body with a range of nutrients during the ‘eat’ period.

 What is keto diet?

Keto diet consists of high fats, moderate protein and very low carbohydrates (55-60% fat, 30-35% protein, 5-10% carbohydrate)[2]. To achieve such a low carbohydrate intake, keto dieters usually consume no breads, grains or cereals. Even fruits and vegetables are to be restricted because they too contain carbohydrates[3]. It places our body in a false fasting state, in which the body is deprived of the primary energy source (i.e. carbohydrate), leading to metabolic changes to avoid new fat storage and to increase breakdown of body fat[2].

Which method is suitable for you?

Intermittent fasting and keto diet have in fact shown effective weight loss with improvements in cholesterol, blood sugar, insulin levels and others in many studies. However, there are factors to consider when you are thinking of trying them out.

Research and Evidence: Intermittent fasting

While intermittent fasting showed effective weight loss in the short term[7], studies also found out that intermittent fasting was not more effective than conventional daily calorie restricted diet – the dropout rates, amount of weight loss, body composition changes and appetite change were found to be similar[4-6]. Compared to other weight loss interventions, intermittent fasting seemed to have lower dropout rate[8], which might be potentially because it has lesser restriction in food choices, giving more freedom for people who practise it.

Since there is no one universal solution, intermittent fasting may be one safe weight loss method to consider. Yet, people with advanced diabetes or who are on medications for diabetes, people with a history of eating disorders, and pregnant or breastfeeding women should not attempt it unless close supervision[9].  It might also be difficult for people who have small and frequent meals, as well as those who have gastric problems[10].  People potentially struggle with the fasting days[9]. Besides that, when people have prolonged fasting periods, it places one at risk for overeating when food is reintroduced and may foster unhealthy behaviours, like binge eating during the cheat days[10], making fasting efforts in vain. In contrast, with conventional daily calorie restricted diet, people progressively reduce excessive food intakes to individualized amounts. If they persevere, good dietary habits may be developed and the diet practice becomes effortless over time.

Studies have shown that intermittent fasting can aid weight loss however it is important to remember that different diets work for different people and fasting may not be suitable for everyone.

You need to consult a qualified healthcare professional before trying it. The problem is, restricting your body for long periods of time can lead you to over eat during the time period that you are able to so it is  important to fast in a way that isn’t too restrictive.

The 16/8 method requires participants to eat within an 8 hour time period over 24 hours and to fast for 16 – this is relatively attainable if you are open to pushing breakfast back to mid-morning (11:30) and to have dinner at 7pm.

Research and Evidence: Keto diet

Keto diet is quite restrictive. Research supports this eating pattern for epilepsy when the diet is supervised by experienced healthcare professional and multi-disciplinary team, since this treatment approach may be complex. However, with regards to the keto diet as a tool for weight loss and other health benefits, the jury is still out[12]. The available research is still limited, and the health benefits only showed to be more effective than the conventional weight loss diets during the first year [11].

Keto diets may potentially cause symptoms like hunger, fatigue, low mood, irritability, headaches, and brain “fog”[11]. Some keto dieters also reported trouble sleeping [12). Due to lack of high fibre rich foods, the diet also increases the risk for constipation [12]. Though these uncomfortable feelings may subside, staying satisfied with the limited variety of food choices and being restricted from otherwise enjoyable local foods like nasi lemak  or roti canai may present new challenges[11]. In addition this, the  negative side effects of a long-term ketogenic diet have been suggested  an increased risk of kidney stones and osteoporosis and increased blood levels of uric acid (a risk factor for gout)[11]. Due to the strict diet restrictions, there are also concerns for nutrient deficiencies such as B vitamins and minerals that are typically found in whole grains. Keto dieters are advised to seek professional advice from a qualified dietitian to minimize nutrient deficiencies [11].

The Bottom Line

While weight loss is important for overall health, we must not lose sight of what is essential, which is the long term safety, effectiveness and sustainability. There are many trending diets that seem to be promising for weight loss, but bear in mind that most studies only looked into short term effects of such diets. The long term safety and effectiveness remain unclear.

Ultimately, the goal is not just to lose weight, but a healthy balanced diet and regular physical activity results in better quality of life and reducing risk of chronic diseases.

We can enjoy our life through healthy and tasty nutritious food while trying to lose weight, by eating in moderation and in smaller portions.



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