Introduction

We all have heard of a diet, and most adults have been on some kind of restrictive diet at some point in their lives, or know someone who has. Weight loss is a desired outcome for many, and an established and expanding commercial industry. Promises of an easy and simple-to-follow plan, yielding accelerated weight loss for a small price, had enticed many of us into handing over our hard-earned money in an attempt to lose weight with minimal effort required on our part. The commercial diet industry is vast, with many different approaches to weight loss strategies available. Do they really work? Or is it just the convenience that tantalises us into purchasing these products and partaking in their regimes?

What is a commercial diet?

A commercial diet is any diet plan or product that is subscribed to and paid for, with the intention of restricting food intake in some form, to produce the desired outcome, a lower number on the scales. Some popular commercial diets that most people have heard of include:

1. Weightwatchers
2. Slimming World
3. Atkins Diet
4. Slim Fast Plan
5. Noom
6. Jenny Craig

This list is by all means not exhaustive, there are hundreds of commercial diet plans available in the UK, with new start-up businesses arising frequently, hoping to tap into this profitable industry.

A commercial diet is popular as it allows users to follow a plan that is already drawn out for them, often customised to a person's own weight loss goals, based on level of activity, lifestyle factors, age and gender. These plans calculate and categorise what an individual should eat in order to achieve their goals, often with an end date in sight. It takes the confusion out of calculating, measuring and combining nutrients independently, meaning these plans are easy to follow. 

We will explore some of these well-known non-commercial diets to assess their efficacy in increasing weight loss success.

Types of commercial diets

There are a wide variety of commercial weight loss diets available. Some of them are strictly low carbohydrate, some are low fat and low calorie and some include meal replacement products. The variety of different diets available is beneficial as some diets may be easier to follow than others in certain individuals, and promote sustainability in the long term. 

Low carbohydrate diets

Low carbohydrate diets such as the Keto (Ketogenic) diet are not a new discovery, high protein diets have been implemented for hundreds of years. The first commercial version of this diet is the Atkins diet, established by cardiologist Dr. Robert Atkins in the 1960s.¹ Interest in this method has continued to develop and is an extremely popular weight loss method currently.

Principles behind a low carbohydrate diet

Generally, a low carbohydrate diet restricts the macronutrient carbohydrate to between 20-50g per day. Following this diet means items such as pasta, potatoes, bread, rice, wheat-containing items, high sugar items such as cakes and pastries are eliminated from the diet. The diet consists of consuming high-protein and high-fat items. Protein includes meat, fish, eggs and nuts. High-fat items include cheese, cream, avocado and olive oil. Some low-carbohydrate leafy vegetables are permitted in a limited quantity, as are small amounts of berries.

The general principle behind this diet includes switching the body from utilising glucose-based energy sources for metabolic activities within the body to a mechanism which uses and burns fat stores. The primary preferred fuel that cells use to perform metabolic processes (burning calories in the meantime) is glucose.

Glucose enters the body via eating sugar, which is essentially a carbohydrate. When we consume carbohydrates, the glucose accumulates in the blood until it is removed via insulin secretion and is then converted by the liver and stored as glycogen for future use and in times of fasting. Wherever there is glucose in the blood or glycogen stores, the body will use this as a primary fuel. When following a very low carbohydrate diet, the body uses and depletes the glucose and glycogen stores, and has to switch to breaking down fat molecules to use as fuel instead. ² The body has now entered what is called a state of ketosis, producing ketones which are easily detectable in the urine, and hence the name Keto diet.

Pros and Cons

A low-carbohydrate diet yields successful results quickly, leading to its sustained and increased popularity. There are advantages and disadvantages of following this regime in the long term.

Advantages

• The diet is easy to follow. Eliminating restricted foods and only consuming nutrients in the “allowed’ list is quite simple to follow
• Satiety is often observed. A high protein and high-fat diet leads to people feeling full, and paradoxical to the expectations of following a diet. Individuals are much more likely to maintain a diet if they are not feeling hungry
• Weight loss is often fast. Quick results are likely to encourage maintaining the regime
• Type 2 diabetes reversal. A low carbohydrate and hence low sugar diet, decreases the requirement of insulin production and has been shown to reverse type 2 diabetes³ 
• Cardiovascular benefits. A reduction in blood pressure, lowering cholesterol levels and improving the longevity of the cells lining the blood vessels are all benefits associated with eliminating sugar from the diet
• The ketones produced for use as fuel exhibit anti-inflammatory properties. Reducing the risk of developing some cancers, neurological diseases and other inflammatory-associated diseases⁴ 

Disadvantages

• The diet is restrictive, eliminating whole food groups may make it difficult to access convenience foods or to socialise in an eating scenario with friends, which could lead to some social isolation
• Constipation is a commonly reported side effect
• Nutritional supplementation is required. By eliminating whole food groups individuals are at risk of developing nutritional deficiencies
• People who have problems eliminating fat in their digestive systems should not proceed with a low-carbohydrate diet. These contraindications include people without a gallbladder and people with liver problems
• The cardiovascular benefits highlighted above may be short-lived. It is yet to be concluded whether these benefits persist in the long term³

Low-fat and low-calorie diets

Following a low-fat and low-calorie diet is the most common weight loss method. Commercial diets such as Weight Watchers and Slimming World adopt these methods in their weight loss plans. Commercial diets take out all of the confusion when calculating calories and fat content, by planning meals for members, and promoting optimum results when followed properly.

Principles behind a low calorie and low-fat diet

It has been believed and advocated for decades that a calorie deficit is required in order to lose weight. Calorie deficit simply means consuming fewer calories than you use. The body is constantly burning calories to fuel general internal metabolic processes. Exercise further increases the amount of calories burnt, hence the reason it is encouraged alongside diet, to further increase the likelihood of weight loss. The recommended daily intake of calories for adults assigned female at birth (afab) is 2000 and for adults assigned male at birth (amab) it is 2500, to maintain a healthy weight.

Most weight loss regimes suggest creating a calorie deficit of 500 calories per day, for example consuming 1500 calories per day as a female, which should lead to decreased weight over time. By adding exercise a person can increase the calorie deficit to accelerate weight loss, or it allows a person to consume more calories whilst still maintaining a deficit. Low fat generally comes hand in hand with low calories due to its health-promoting benefits. Additionally, low-fat foods contain fewer calories, meaning that the quantity of these foods is often not as limited as higher fat products. The commercial diet industry has taken all of the science necessary to successfully follow these diets out of the equation, by formulating instructional plans for individuals to achieve successful weight loss outcomes.

Pros and Cons 

A low-calorie and low-fat diet is the most widely accepted type of diet, with Doctors and other Healthcare Professionals advocating, advising and prescribing this method in order for individuals to maintain a healthy BMI as well as a healthy internal body environment and increase longevity.

Advantages

• There are a lot of commercial diets out there that utilise the principles in their plans, leading to a variety of different choices. So, if for instance, one diet plan does not suit an individual, there are others to attempt which may be more suitable
• It is easy to follow. With commercial diet plans providing easy-to-follow meal plans and options, including a weekly shopping list in some cases, it takes all of the research and calculating out of the equation
• There is an abundance of convenience foods available in shops, supermarkets, and restaurants that people are able to consume whilst embarking on this type of diet. This increases the chance of people being able to stick with the plan in the long term. This is especially advantageous for busy people who often do not have the time to prepare meals from scratch
• It does not exclude whole food groups, unlike the low carbohydrate diet. Meaning it is nutritionally balanced, decreasing the likelihood of nutritional deficiencies
• Increased immune functioning. Calorie restriction increases the production of T cells; infection and cancer-fighting cells⁵ 
• Substantial weight loss can lead to a reversal of type 2 diabetes
• Heart health is increased. Studies have shown that decreasing weight via a low-calorie and low-fat diet can decrease heart age by as much as 15 years. Reducing cholesterol via limiting unhealthy fats, decreases the risk of heart disease and stroke⁶

Disadvantages

• Following a low-calorie diet often means eating substantially less, leading to hunger. If an individual is feeling perpetually hungry, they are not very likely to sustain the diet in the long term
• Transient constipation, fatigue and headaches are common in the first few days
• Very low-calorie diets (VLCD) are becoming increasingly popular and are available commercially. Commercial diets include a fasting diet, restricting calories to as little as 600 per day for a short period of time. The results from studies on VLCD have mixed results. Following a VLCD for a short period of time, for example, 5 days, has been shown to provide very positive results. However, unregulated and prolonged VLCD can be damaging and even fatal in some cases. Severe dehydration and malnutrition can ultimately lead to heart failure and death

Meal replacement

There are many meal replacement products on the market. Meal replacement provides the ultimate convenience, however it is the most expensive type of commercial diet to follow. Meal replacement includes pre-prepared meals and snacks, and sometimes meal replacement drinks such as shakes. The consumer does not have to plan, shop or prepare any food whilst on these plans, as everything is provided. Meal replacement companies often offer a variety of plans to suit the individual. You can often select from low carbohydrate, low calorie and low fat.

Furthermore, they take dietary requirements and preferences into consideration such as; plant-based menus, dairy-free, gluten-free etc. Meal replacement is a favourable option for busy people who do not have the time to shop, plan and prepare food daily in order to maintain a long-term diet. Therefore, the likelihood of sustaining a diet regime of this sort is increased due to convenience.

Summary

The commercial diet industry is well established and continues to report increased profits year on year. With more people becoming overweight and obese every year, attempts at weight loss in general are increasing, with people turning to commercial diets due to their easy-to-follow guidelines together with their accessible products. On the whole, commercial diets do work in that people can lose weight if they can stick to the prescribed regime.

With an abundance of companies out there offering different products, it is possible for people to find a plan that suits their own preferences and lifestyles. Once a person has achieved and reached the desired outcome or “goal weight" they must attempt to maintain it.. Many commercial diet companies have taken advantage of the maintenance phase, where plans that are less restricted are advised so that a person can maintain their goal weight in the long term. The maintenance phase is a difficult phase, as it requires a person to follow the guidelines for the foreseeable future, which can be daunting.

Knowledge of what nutrients and in what quantity are required both to lose weight and to keep the weight off is advisable. This way a person can tailor their own diet plan to suit their own preferences, which may be more sustainable in the long term due to fewer restrictions on certain items, with the focus being on moderation and making healthy choices. A commercial diet is a good starting point for individuals who do not have any knowledge of what they should be eating, how much and when they should be eating it. In the long term, education is key so that people can make their own informed choices during the course of their lifetime, promoting health, longevity and an increased quality of life.