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Why Fad Diets, Such As Very Low Carbohydrate, Are Not The Answer To Healthy, Long-term Weight Loss

Holly Lehmann is a Registered Associate Nutritionist specialising in weight loss and behaviour change. She is the founder of Eat Better with Holly that offers a unique and personalised weight loss programme, 'Eat Better Feel Better.'

Executive Contributor Holly Lehmann

As dieting has become more and more popular in the last two decades, any new and noteworthy fad diet seems to make the rounds quite quickly, especially on social media! However, fad diets are not necessarily the key to healthy, successful, long-term weight loss and the downsides can outweigh the upsides! Let’s take a look.

Person hand wrapped by tape measure

What is a fad diet?

Fad diets tend to pledge rapid weight loss. They usually have a phase of popularity and turn into a trend. There are many fad diets out there, such as; low-carbohydrate, ketogenic, low-fat, juicing, high-protein, detox, paleo, Atkins (just to name a few). Some fad diets boast a no exercise regimen, others may cut out certain (important!) food groups whereas others may heavily focus on one type of food (e.g. cabbage soup diet). 

What are the problems with fad diets?

  • Yes, fad diets tend to lead to rapid weight loss (at the beginning) but this is usually down to the loss of water and lean muscle mass and not body fat! On a low carbohydrate diet, where carbohydrate intake is low or very low, the body turns to its glycogen stores. Glucose (a building block of carbohydrate) is stored as glycogen. Each stored gram of glucose is stored with around 3 grams of water. This explains why low carbohydrate diets can lead to rapid weight loss in the first weeks; water is lost whilst glycogen stores are used and depleted for energy (glucose!).

  • They don’t support and help an individual prepare for long-term dietary and lifestyle changes. Therefore, alongside their restrictive food intake, they are usually very unsustainable in the long-term.

  • Cutting out certain food groups (e.g. dairy, legumes) may not only lead to nutritional deficiencies but some dieters may start to believe that such foods are ‘harmful’. Long-term, this may hinder the development of healthy dietary habits.

  • Fad diets can result in weight cycling, known as the yo-yo effect. A sudden reduction in calories (not unusual on such diets!), is unexpected for the body. It comes as a bit of a surprise. Consequently, the body feels it needs to adapt quickly. It, therefore, changes the speed of its metabolism in order to preserve energy. The body’s metabolism slows down. This may be contrary to what many dieters think or hope for! As calorie-restricted diets are difficult to follow long-term (for many reasons), individuals usually stop the diet and resume their previous dietary habits and calorie intake. However, it now takes time for the body’s metabolism to change back to what it used to be. This is why the influx of calories can lead to fast weight regain and as per research, 1 in 3 dieters regain more weight than they lost.

The difference between low and very-low-carbohydrate diets

When someone says they are on a low carbohydrate diet, it’s interesting to ask by how many grams they have cut down on as this varies from person to person. A low carbohydrate diet generally consists of consuming between 60 – 130 grams per day, whereas intake on a very low carbohydrate diet is usually under 50 grams per day to trigger ketogenesis. The ketogenic diet is a very low carbohydrate diet.

The ketogenic diet explained

The ketogenic diet (keto diet) is a popular form of a very low carbohydrate diet, widely promoted for weight loss. What many dieters may not know, is that the keto diet was actually created back in 1923 by Dr. Wilder to treat epilepsy. This article, however, focuses on this diet’s impact on weight loss only, not on epilepsy or any metabolic conditions such as diabetes.

The make-up of the keto diet tends to focus on a daily calorie intake of 5-10% carbohydrate, 20-25% protein and 65-80% fats. This is around double the amount of fat intake that is currently recommended by public health guidelines; no more than 35% fat. Glucose (deriving from the breakdown of carbohydrate) is the body’s man source of fuel, especially for the brain because fatty acids cannot cross the blood brain barrier. The brain needs around 130 grams of glucose per day.

Glucose is in short supply on the keto diet, so the body turns to gluconeogenesis (its own system for making glucose). However, the process of gluconeogenesis is not enough to endlessly provide the body with the glucose it needs. Consequently, the body goes into a state known as ketosis, to produce ketone bodies. These ketone bodies act as a substitute for glucose. Ketone bodies are produced by breaking down fat. The body therefore turns to fat as its main source of fuel. Surely fat breakdown is what dieters want; so why does this type of diet come with concerns?

Possible pitfalls of a ketogenic diet

Despite its popularity, there are some concerns individuals should be aware of.

  • Individuals may experience short-term side effects, such as; feeling nauseous, needing to vomit, feeling lethargic or fatigued, feeling dizzy, experiencing gastrointestinal disturbances, heart palpitations, hair loss and/or a dry mouth.

  • The high-fat content of the diet, from animal sources, may increase LDL cholesterol (the bad cholesterol) and overall acidity in the body. The high acidity may be problematic for those with underlying kidney problems.

  • The diet is very low in fibre, which can lead to constipation and a shift in the gut microbiome. A low fibre intake can diminish certain important gut bacteria, such as Bifidobacterium. Reduced Bifidobacterium may increase the risk of colonic diseases (the colon is also known as the large intestine). Fibre gets fermented (in other words, eaten) by the gut bacteria in the large intestine, and short-chain fatty acids are produced. These play a crucial role in keeping the mucosal wall of the intestines healthy and intact. A damaged intestinal barrier can allow harmful substances, such as bacteria and toxins to enter the bloodstream, causing inflammation in the body.

  • The reduced consumption in fruit and vegetables leads to a lower intake in vitamins and antioxidants, which are beneficial for cardiovascular health.

How successful are low-carbohydrate and very-low-carbohydrate diets for weight loss?

The National Lipid Association Nutrition and Lifestyle Task Force published a review in 2019 based on multiple meta analyses, evaluating the impact of low carbohydrate and very low carbohydrate diets on weight loss. The authors report that these types of diets are not just difficult to maintain but are no better than other types of diets for weight loss. At 6 months, they tend to lead to greater weight loss compared to higher carbohydrate diets but long-term (>6 months), there is either minimal difference in weight loss or weight loss is the same.

A 12-month randomized clinical trial by Davis and colleagues compared the effect of a low-carbohydrate diet to a low-fat diet on weight loss in 105 overweight diabetic participants. In the third month, the average carbohydrate intake in the low carbohydrate diet group was 24% of total energy intake. This increased to 33.4% in the twelfth month, suggesting challenges in adhering to a restricted carbohydrate intake. In the low-fat diet group, the average carbohydrate intake in the third month was around 53% of total energy intake and around 50.1% in the twelfth month.

Results found that:

  • Participants on the low carbohydrate diet lost more weight after three months.

  • After one year, there was no longer a significant difference in weight loss. Average weight loss in both diet groups was around 3.4% , despite participants in the low-fat diet group having consumed more carbohydrates.

Weight loss is about a lifestyle change

In conclusion, fad diets are trendy diets that are typically challenging to adhere to long-term, They are usually very calorie restrictive or omit too many food groups, which can become frustrating over time, especially in social settings. Low-carbohydrate and very low carbohydrate diets tend to lead to greater weight loss at 6 months compared to non-restrictive carbohydrate diets. However, after 6 months, there is mostly no longer a difference in weight loss.

Weight loss and long-term weight loss maintenance is not about cutting out one of the macronutrients (carbohydrate, protein, fats), being overly restrictive, feeling frustrated or hungry all the time. Instead, it’s about learning how to reduce overall calorie intake by replacing high-energy-dense foods (high-calorie foods) with less energy-dense foods (low-calorie foods). Finding new dietary habits that can be enjoyed and adhered to long-term. Learning and understanding what impact nutrition can have on our overall health. This is the approach my ‘Eat Better Feel Better’ weight loss programme takes, as well as taking clients’ individual food preferences and personal lifestyles into consideration.

A discovery call can be arranged with me; click here, where you can find detailed information about the programme ‘Eat Better Feel Better’.


Read more from Holly Lehmann


Holly Lehmann, Nutritionist

Holly Lehmann, Registered Associate Nutritionist, is passionate about helping others optimise their diet and lifestyle to lose weight, maintain weight loss and feel healthier and happier overall. Before changing career to become a qualified Nutritionist, Holly worked in management positions in the luxury hotel sector for around 10 years. She is fully aware of how shift-work and long-working hours may lead to poor dietary habits. Her personalised weight loss programme, 'Eat Better Feel Better' is tailored to each individual client, taking their lifestyle into consideration and supporting them in changing any poor dietary habits into long-lasting, beneficial ones.



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