We are often told that the following diets are the solution to our weight loss goals. But do they really work?
Below we examine the evidence behind the top five diets, as well as what might work better.
A keto diet involves the reduction/ elimination of carbs so that the body starts to produce energy from ketone bodies- instead of glucose. A keto diet is pretty high in fat/ protein which is surprising to some as a weight loss strategy.
A ketogenic diet has proven very effective against conditions such as epilepsy and certain brain cancers, and it can promote weight loss in certain individuals. This is because, when we eliminate or greatly reduce our carb intake, we also reduce our production of insulin.
Insulin is responsible for the transportation of glucose into the cells for storage, and therefore if energy is not immediately required, this glucose accumulation can promote weight storage.
Without carbs, this does not happen. Also, the body will start to use up any stored glucose before it turns to make energy from the fats, again, promoting a reduction in weight loss.
However, keto diets are not for everyone, they can impair cognitive function, cause issues with glucose regulation, and lead to a reduction in beneficial fibres. This kind of diet can be a good short-term option for quick weight loss, but in the longer term, most people need to introduce some amount of carbs to offset the side effects.
2. High protein
A high protein diet sounds promising, as it naturally leads to the reduction in carbohydrates, which can reduce circulating insulin levels, and therefore reduce excess weight loss. However, in high quantities protein can cause weight gain too; it is higher in calories than carbohydrates and promotes insulin production in excess.
The benefit of a good intake of protein is that it helps the body reach its own inbuilt ‘protein target’. This is where the body encourages you to keep eating until this limit has been met. If we eat enough protein then we reach this target sooner, preventing overeating and possible weight gain.
However, we do not need a super high protein intake for this to happen and considering excessive protein intake can be challenging for the kidneys to process, it may be better to moderate protein intake to more reasonable levels, in line with low-medium intake of complex carbs, and moderate intake of healthy fats.
3. Low fat
This seems like the obvious diet of choice; it is lower in calories by default, and it reduces our intake of foods such as steak and full fat dairy which we typically associate with weight gain. However, when we go ‘low fat’ we may accidentally end up also going high sugar. This is because many products labelled as low fat- for example yoghurts and other processed snacks use added sugar to restore flavour and texture.
This can lead us to consume foods which promote insulin production and encourage weight gain. Indeed, the act of eating a piece of steak of a portion of yoghurt does not promote fat storage. It is actually when we combine these fats with processed refined carbs, such as chips or cereals that weight gain becomes a concern.
In addition, we need certain fats for health, they are essential, and the body cannot make enough of its own – in particular this applies to omega 3 fats which we need for heart and brain health. If we cut back on oily fish, walnuts, olives, and other forms of heart healthy fats we can risk a hormonal imbalance and increased inflammation, both of which increases our risk of weight gain.
Instead, by focusing on a moderate intake of polyunsaturated fats we can promote our health without effecting our weight.
4. High carb
This rationale behind this diet is that because it reduces both protein and fats, it will be less high in overall calories. There are 9 kcal per gram of fat and protein but only 4kcal per gram of carbs, which explains this logic.
However, this is not taking into account the issue of metabolic processes, and as we have already discussed- the role of insulin in promoting weight gain.
Even if we are reducing calorie intake via eating more carbs, we are more likely to store these carbs than proteins or fats.
In fact, it was the shift from fats to highly processed carbs in the 1950s which actually led to a huge rise in obesity rates- and the corresponding metabolic disease we see today.
5. Low calorie
A common diet is simply a calorie restricted one. This makes sense in many ways and fits in with the popular model of weight loss which is calories in < calories out. However, unfortunately it is not usually this simple.
Low calorie diets are often in the region of 800 calories a day, which make them pretty challenging to stick to.
But very low-calorie diets do, at first, appear successful. Weight loss often occurs reasonably rapidly, making followers feel encouraged to continue. However, this initial weight loss is mostly comprised of water and glycogen, rather than body fat.
Even more annoyingly, this type of diet leads to a plateau- where the weight just stops decreasing, leading participants to feel deflated and personally responsible for its failure.
However, it is very much not the fault of the individual, as the body has its own inbuilt defence mechanism against prolonged calorie restriction. It sees extreme food reduction as a threat, and both decreases energy expenditure whilst increasing appetite. This leads to the ‘plateau’ which we blame ourselves for, but really shouldn’t.
In fact, studies show that when these types of diet are followed people tend to end up weighing more on average a year after the diet, than before they began, making them a poor choice for sustained weight loss.
A mild calorie restriction can avoid this problem, and is much more achievable in the long term, promoting sustainable weight reduction.
- Each of the above diets has pros and cons but there is no magic cure when it comes to weight loss
- Low calorie diets may work at first but are subject to an inevitable plateau
- A carb reduced diet appears one of the best ways to achieve sustainable weight loss over the longer term
1 Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a low-carbohydrate diet for obesity. N Engl J Med. 2003. doi:10.1056/NEJMoa022207
2 Strowd RE, Cervenka MC, Henry BJ, Kossoff EH, Hartman AL, Blakeley JO. Glycemic modulation in neuro-oncology: Experience and future directions using a modified Atkins diet for high-grade brain tumors. Neuro-Oncology Pract. 2015. doi:10.1093/nop/npv010
3 Kang HC, Chung DE, Kim DW, Kim HD. Early- and late-onset complications of the ketogenic diet for intractable epilepsy. Epilepsia. 2004. doi:10.1111/j.0013-9580.2004.10004.x
4 Weigle DS, Breen PA, Matthys CC, et al. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Am J Clin Nutr. 2005. doi:10.1093/ajcn.82.1.41
5 Hu T, Mills KT, Yao L, et al. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: A meta-analysis of randomized controlled clinical trials. Am J Epidemiol. 2012. doi:10.1093/aje/kws264