There are hundreds of powders, gels and bars that promise to improve an athlete’s performance. But judging which ones are based on good scientific evidence and which might be useful for a particular activity or individual is a bewildering business.

Even the fact that professional sports teams use particular products might not be an indicator of their effectiveness – they may merely be fulfilling their sponsorship obligations.

Stephen Mears, a lecturer in sport and exercise nutrition at Loughborough University, advises athletes to get their diet right first before they start resorting to supplements. He also warns users to read the packaging carefully. “Some of these products are vague or make no claims on their packaging. This is something you should be wary of as a consumer.” Often the marketed active ingredient isn’t causing the effect you feel – many of these products produce their kick with caffeine.

One of Mears’s colleagues, Professor Ron Maughan, has a rule of thumb: “If it works it’s probably banned, if it’s not banned it probably doesn’t work, but there may be a few exceptions.”

So are any of these products the exception to the rule? We asked Mears for his expert view.

Myprotein Organic Beetroot powder, 200g £9.99

Myprotein Organic Beetroot powder. Photograph: Katherine Anne Rose/The Observer

Manufacturer’s claim It’s a fantastic source of protein, which contributes to the growth and maintenance of muscle mass, and it’s also low in fat, as well as being high in fibre – an important part of any healthy, balanced diet.

Expert view A lot of athletes take shots of concentrated beetroot juice around two to three hours before a race. Taken that way it tends to open up the nitric oxide pathway, which allows you to deliver oxygen to the muscles more easily as you speed up your V0 2 kinetics. There is good evidence that it works – it is especially good for something like a 1,500m or 3km run or a 10-mile time trial on a bike. I’m not sure about beetroot in powder form. It is marketed as a protein source – however, if you ingested this entire packet you’d only be taking in 22g.

SiS Whey20 mixed pack strawberry & lemon, 4x78ml, £8

SiS Whey20

Manufacturer’s claim Provides an innovative protein delivery system without the need for a shaker or water.

Expert view Protein is normally a recovery aid, you need it for muscle growth and repair. So it helps after exercise. However, you don’t really need to ingest protein within two hours of exercise as many people think. There’s evidence that the anaerobic window may last for 24-48 hours after exercise. So you don’t have to race home for protein. What research does advocate is having lots of doses throughout the day.

The general belief is that 20-25 grams per dose is what your body can manage, but there’s some recent evidence that if it’s whole body exercise – where you are using lots of different muscles – you can take up to 40g. Excess protein just gets excreted. The guidelines are that endurance athletes need 1.2-1.4g of protein per kilo of body weight a day, strength athletes require 1.4-1.8g.

These are more for convenience. You can drop them in your bag and take them wherever. These would be quite good for any athlete. Often endurance athletes can underestimate the amount of protein they require.

OTE Beta Alanine

Manufacturer’s claim Ideal for anyone participating in sports that are explosive, such as sprinting or weight training, and for those involved in prolonged endurance exercise.

Expert view When you do high-intensity exercise you produce lactic acid because you’ve not got enough oxygen – which results in a burning sensation in your muscles. Beta alanine is a precursor to carnosine which acts as a buffer to the burn. This isn’t a one-shot supplement, you need to take 2-4g per day for a number of weeks before you begin to see benefits.

This is one of the few products that does have some evidence behind it. It is particularly useful for one- to four-minute events, such as 1-2km rowing, cycling time trials or runs up to 3km. But there may be some side effects, such as a tingling feeling in the fingers.

Holland & Barrett Tribulus Terrestris

Manufacturer’s claim Contain natural steroidal chemicals called saponins, the active ingredient in Tribulis terrestris, which is thought to promote sexual desire and sexual capacity. It’s also good for maintaining the health of the respiratory system and having a soothing effect on the nervous system. This supplement is widely used by bodybuilders for its effects.

Expert view This is a precursor to testosterone. There is no evidence that it improves performance in humans. If it caused spikes in testosterone it would be illegal in competition. The testosterone product men are prescribed by doctors is a product that has been proven to work in clinical studies. Any perceived benefits of this product are likely to be psychological.

Stealth Keto Energy Gel (coffee), £40 for 14

Stealth Keto Energy Gel

Manufacturer’s claim Low-carb energy gel, almost instant ketosis. Intended to meet the needs of intense muscular activity.

Expert view Athletes sometimes want to promote a state of ketosis. By reducing carbohydrate intake they can promote use of other fuels such as ketone bodies. This product aims to do that through medium chain triglycerides (MCT). After water the next most abundant ingredient in this gel is MCT – this is a source of fat that will hopefully spare carbohydrate and promote ketosis.

Participants in studies ingesting large amounts of MCT’s have often found themselves running to the toilet a lot – however the use of an emulsifier in this product should increase tolerance. An alternative is to take an external source of ketone esters. Ketone esters are a source of fuel within the body and if you can enhance them you can potentially spare carbohydrates. A group of scientists in Oxford have tried to produce a different product containing ketone esters that will help spare carbohydrate; these have been shown to enhance 30-minute cycling performance but their product isn’t on the consumer market yet.

As this is a keto energy gel these list 11.5g of fat – this is the MCTs and only 11g of carbohydrate per gel – although this is made up of soluble fibres rather than sugars. This combination is designed to encourage ketosis. Ingestion of this product is likely to work but make sure you try them in training to see if they suit you before you take them in a race.

* This article was amended on March 27 to correct the amount and type of carbohydrate in the Stealth Keto Energy gel