When it comes to weight loss a quick fix isn’t always the right fix. Fad diets are commonly shared on social media channels like Tik Tok and Instagram with many people raving about their success. While some people may see short-term weight loss, most research clearly shows that the most restrictive diets make weight loss challenging to maintain in the long-term (1,2). Fad diets are often not sustainable for life and can cause people to regain their lost weight back and sometimes even more than their starting weight (1,2).
We know that it can be easy to fall into a dieting-binge-dieting cycle. Below we’ve covered 5 popular diets and our nutrition experts have given their take on the nutrition, sustainability and impact on weight loss, health and wellbeing.
The Ketogenic Diet
The keto or ketogenic diet is one of the most talked about diets. It claims to support weight loss, diabetes management and improve overall health. However, the research around the long-term benefits and consequences of this dietary approach are unclear. In fact, a recent meta-analysis suggests that a ketogenic diet increases low density lipoprotein cholesterol and total cholesterol (5).
Keto is extremely restrictive with the diet requiring almost full elimination of dietary carbohydrates (less than 50g carbohydrate per day). Not only are you expected to cut out your beloved bread, but even some fruits are labelled as a no-go food! By cutting out a whole food group, it can decrease your fibre intake as wholegrains are restricted. Wholegrains and fibre help to make us feel fuller, and a diet containing these foods has actually been shown to support weight loss and improve overall health (3).
Another principle of keto is replacing carbohydrates with fat, resulting in increased fat intake. Long-term, this can increase cholesterol and heart disease risk if the increased fat intake is saturated fat (typically coming from animal products) (4). A common symptom of the keto diet is the ‘keto flu’ which creates flu-like symptoms such as fatigue, headaches, fainting, and bowel issues – doesn’t sound fun, right! Others have claimed the diet can help with mental clarity and improve focus, however, there is limited evidence to support this.
Intermittent Fasting
Intermittent fasting has gained popularity, and involves planned and usually long periods of time, of not eating. One of the most well-known versions of this diet is the 5:2 diet, where you will eat ‘normally’ for five consecutive days, followed by two days of drastically reduced food intake.
Like other restrictive diets, this can result in quick weight loss, however it’s not just about when you eat, it’s also about WHAT you eat. The ‘normal’ eating days don’t translate to a free pass for unlimited junk food. A balanced diet with plenty of colourful vegetables, wholegrains and quality proteins is still key.
Some people will swear by intermittent fasting, that it improves focus and energy, and is reasonably easy to stick to. But for others, the side effects are less than appealing. Extreme hunger, dizziness, low energy and headaches are just a few of the main ones (6). This diet certainly is not for everyone, especially those people who have insulin dependent diabetes or people who have certain health conditions or medications which rely on regular food intake (7).
Juice Cleanse or Detoxes
You may have heard of a juice cleanse with many celebrities and influencers hopping on the trend to detox their body. However, the juice cleanse has been known to do more harm than good. Juice detoxing not only makes you ‘hangry’ but also has little benefits to your body and can also cause uncomfortable bowel issues in some people! The low energy intake of a juice cleanse will likely cause some initial weight loss due to the decrease in water weight. However, once you return to your normal diet the weight tends to return (8).
There are also claims a juice cleanse has detoxification benefits. But our incredible bodies already have a natural detox process which does not need assistance by putting yourself through a juice cleanse (9,10). The current evidence suggests that a juice cleanse will also likely result in headaches, fainting, weakness, fatigue, and irritability (11). Next time you consider doing a juice cleanse, think twice and your body will thank you for it.
Gluten Free Diet
Over recent years the gluten free diet has been considered a tool to lose weight or improve health. However, there is no consistent evidence to suggest that a gluten-free diet can support weight loss (12,13).
It’s important to only follow a gluten free diet when diagnosed with coeliac disease or wheat or gluten intolerance or allergy. A gluten free diet can result in vitamin and mineral deficiencies, and poor bone health due to the diet being traditionally lower in fibre, and gluten free flours typically containing less enriched vitamins and minerals (10,12).
There is a common misconception that gluten free food products are healthier however this is not the case. While gluten free products are more expensive, they are often more processed, lower in dietary fibre and higher in sugar and fat (12). Before making any major changes to your diet it’s always important to consult with your doctor, dietitian, or registered nutritionist and based on your individual symptoms and health needs.
Carnivore Diet
The carnivore diet removes almost all foods that don’t come from animals. This often means none (or very little) fruits, vegetables, grains, nuts or seeds – and mostly meat, chicken, eggs and dairy. While animal products provide important nutrition like iron, zinc and protein, relying solely on these means you’ll likely miss out on essential nutrients, minerals, fibre and antioxidants which are found in plant foods (13). Fibre is the key to healthy digestion, gut health, managing blood sugar levels and overall health.
Along with this, given the carnivore diet is based around animal products (some of which may be processed), this diet is likely to contribute higher than recommended amounts of saturated fat and sodium, which can increase risk of heart disease (13).
There are theories that people who feel ‘better’ after doing the carnivore diet, are experiencing this due to cutting out a wide range of foods (not the benefit of eating mostly animal products). At the end of the day, the carnivore diet is unsustainable, and likely to cause nutrient deficiencies and have long term impacts on health. It’s always best to consult with your health care provider for professional advice before following any kind of restrictive diet.
Unfortunately, although they can seem like an easy fix, if you do want to lose weight a fad diet might not be the answer. It’s important to create healthy habits that are achievable and maintainable that help create long-term weight loss and wellness goals. Every food is healthy in moderation.
References:
- Hooper, B. (2014). Popular diets – what is the evidence? Nutrition Bulletin, 39(3), 284–289. https://doi.org/10.1111/nbu.12104
- McBean, L. D., & Speckmann, E. W. (1974). Food faddism: a challenge to nutritionists and dietitians. The American Journal of Clinical Nutrition, 27(10), 1071–1078. https://doi.org/10.1093/ajcn/27.8.1071
- Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019 Feb 2;393(10170):434-45. doi: 10.1016/S0140-6736(18)31809-9. Epub 2019 Jan 10. Abstract available from: https://www-ncbi-nlm-nih-gov.ezproxy.massey.ac.nz/pubmed/30638909
- Mansoor N, Vinknes KJ, Veierod MB, Retterstol K. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr. 2016 Feb;115(3):466-79. Abstract available from: http://www-ncbi-nlm-nih-gov.ezproxy.massey.ac.nz/pubmed/26768850
- Chen S, Su X, Feng Y, Li R, Liao M, Fan L, Liu J, Chen S, Zhang S, Cai J, Zhu S, Niu J, Ye Y, Lo K, Zeng F. Ketogenic Diet and Multiple Health Outcomes: An Umbrella Review of Meta-Analysis. Nutrients. 2023 Sep 27;15(19):4161.
- Shalabi, H., Hassan, A. S., 4th, Al-Zahrani, F. A., Alarbeidi, A. H., Mesawa, M., Rizk, H., & Aljubayri, A. A. (2023). Intermittent Fasting: Benefits, Side Effects, Quality of Life, and Knowledge of the Saudi Population. Cureus, 15(2), e34722. https://doi.org/10.7759/cureus.34722
- Hursthouse, N. (2020, July). Which diet is right for you? Heart Foundation NZ, Retrieved 2025,
- Klein AV, Kiat H. Detox diets for toxin elimination and weight management: a critical review of the evidence. J Hum Nutr Diet. 2015 Dec;28(6):675-86. doi: 10.1111/jhn.12286. Epub 2014 Dec 18. PMID: 25522674. Abstract available from: https://pubmed-ncbi-nlm-nih-gov.ezproxy.massey.ac.nz/25522674/
- Is a “Juice Cleanse” Right for You? (2022). Tufts University Health & Nutrition Letter, 40(4), 3. Here are some of the key features of this dynamic service to ensure that you have the latest information about food and nutrition at your fingertips (massey.ac.nz) Evidence PEN
- Can Gluten-Free Foods Help Aid Weight Loss? – Cleveland Clinic
- Marcason, W. (2011). Is there evidence to support the claim that a gluten-free diet should be used for weight loss? Journal of the American Dietetic Association, 111(11), 1786. https://doi.org/10.1016/j.jada.2011.09.030
- Practice-based Evidence in Nutrition and Case S. Are you being asked about the benefits of going gluten-free for weight loss?
- Goedeke, S., Murphy, T., Rush, A., & Zinn, C. (2025). Assessing the Nutrient Composition of a Carnivore Diet: A Case Study Model. Nutrients, 17(1), 140. https://doi.org/10.3390/nu17010140
