Surprised woman holding up half grapefruit
The New Grapefruit Diet?

The old 'miracle' grapefruit diet has been dismissed as a fad. But eating grapefruit as part of a healthy, balanced diet may give your weight loss a boost.

Eat Grapefruit and Lose up to 10lb?

Reviewed By Dietitian Juliette Kellow BSc RD

The 80s might bring back fond memories of leg warmers, Flashdance and Duran Duran videos, but for anyone who was battling the bulge at the time, it probably also conjures up images of eating vast amounts of grapefruit! If you wanted to lose weight fast, the grapefruit diet was the plan to follow.

Providing no more than 800 calories a day, the grapefruit diet menu involved eating lots of 'fat-burning' grapefruit to kick-start your metabolism, as much black coffee as you liked, some daily protein (mainly boiled eggs) and the odd piece of dry toast.

At the time, nutrition experts dismissed it as another fad diet, explaining that the 'fat-burning' properties of grapefruit were, in fact, a myth and any weight loss that occurred was due to the extremely low and potentially dangerous calorie intake.

But two decades on, it seems these nutritionists may need to rethink their views on the popularity of grapefruit as a 'diet food' if the results of a study published earlier this year are to be believed.

The latest research, carried out by scientists at the Nutrition and Medical Research Centre at Scripps Clinic in San Diego, America, has found that the simple act of adding grapefruit and grapefruit juice to your diet, really can aid weight loss.

But unlike the seriously restricted diet of the 80s, you get these results without changing what else you eat!

Even study leader Dr Fujioka seemed surprised, saying,

'For years, people have talked about the grapefruit diet. Now we have data that grapefruit helps weight loss. Our study participants maintained their daily eating habits and slightly enhanced their exercise routine. The only dietary change was the intake of Florida grapefruit and grapefruit juice.'

This sounds amazing! What else can you tell me about the research?

The study included 100 obese people who were divided into three groups:

  • The first group ate half a grapefruit before each meal three times a day
  • The second group drank grapefruit juice before each meal
  • The third group received no grapefruit

No other changes were made to participants' diets.

After 12 weeks, those participants who ate grapefruit with each meal lost, on average 3.6lb. Only a third of a pound a week, but pretty good considering they didn't make any other changes to their diet.

Meanwhile, those who drank grapefruit juice three times a day lost 3.3lb in the 12 weeks.

By comparison, the grapefruit-free participants lost, on average, only 0.5lb.

But weight loss wasn't the only health benefit seen when grapefruit or the juice was consumed.

The research also found the grapefruit-consuming participants had lower levels of insulin, a hormone that regulates blood sugar levels and fat metabolism, which in turn might help to reduce the risk of diabetes or stroke.

What's the theory?

The researchers believe grapefruit contains unique plant compounds that reduce insulin levels, which in turn promotes weight loss.

The link between raised insulin levels and excess weight is complicated and multifaceted: 

  • To start with, high levels of insulin may indicate that sugar isn't efficiently utilised for energy with the result that it's more likely to be stored as fat.
  • Secondly, high levels of insulin can make people feel hungry so that they eat more 
  • And finally, high levels of insulin prevent the body from breaking down fat 

Add these together, and it's easy to see why lower levels of insulin may promote weight loss. What exactly it is in grapefruit that has this insulin-lowering effect remains unclear.

What do the experts think?

Care needs to be taken when interpreting the results. It's the first study of it's kind and even the researchers believe more work needs to be carried out before recommendations are made regarding grapefruit intake.

When it comes to reducing the risk of diabetes, experts also believe we should err on the side of caution before recommending vast amounts of grapefruit.

Speaking to Chemistry & Industry Journal, who published the results of the study, Emma Bunn, diabetes care advisor at Diabetes UK said,

'If grapefruit does significantly lower insulin levels this could be a potentially exciting discovery. We will be following any further research in this area closely to establish if grapefruit could provide genuine benefits.'

Nutrition experts also agree that more research is needed before rushing out to stock up on grapefruit. Most tend to agree with the nutritionalists of the 80s and say it's unlikely that grapefruit has any magical properties in terms of aiding weight loss in the absence of other diet or lifestyle changes. It's perhaps more likely that participants lost weight simply because they were taking part in a study and, as a result, were more focussed on their food intake and exercise habits.

Juliette's verdict

This is an interesting piece of research but even if the results aren't yet conclusive, one thing is certain - eating more grapefruit won't damage your health and can certainly contribute to a healthy diet. (Although, if you are currently taking any medicines, take note of the warning below.)

It's important to eat five portions of different fruit and vegetables each day to keep us healthy and slim and half a grapefruit or a glass of grapefruit juice can contribute to one of these portions.

If you enjoy grapefruit, in most cases it won't do any harm to eat it regularly - but make sure you still include plenty of other fruits and vegetables in your diet as well.

That's not to say I would welcome a return of the 80s-style grapefruit diet - it's way too low in calories, extremely restrictive, unbalanced and, let's face it, incredibly boring!

Twenty years of nutrition advances have taught us that eating a wide range of foods is the best way to lose weight.

As always, if you want to shift those pounds safely and keep them off for good, you shouldn't go below 1,100 calories a day or follow an unbalanced diet that restricts the majority of foods while encouraging vast quantities of just a few.

Warning! Grapefruit juice can interact with medicines

While this research might tempt you to fill up on grapefruit to boost your weight loss campaign, if you’re taking any medications you might want to speak to your GP first or check the literature that comes with your medication.

This is because a wealth of research shows that grapefruit juice can interact with a number of medications, potentially causing serious side effects. It works by inhibiting an enzyme in the intestines that’s responsible for the natural breakdown and absorption of many medications. When the action of this enzyme is blocked, blood levels of these medications increase and this can lead to potentially toxic side effects.

Research suggests that flavonoids and/or furanocoumarin compounds are the substances in grapefruit juice that block the enzyme in the intestines. Many drugs appear to be affected by grapefruit juice so if you are taking any medication, it’s essential to check whether you can safely consume grapefruit juice. In the meantime, it’s likely that grapefruit segments may also interact with certain medications so you’d be wise to consult your GP before eating lots of grapefruit. Other citrus fruits don’t seem to have any effect.

Easy Squeezy Ways to Get Grapefruit into Your Diet


  • Have half a grapefruit for breakfast - it's virtually fat free and contains just 35 calories. Sprinkle over artificial sweetener rather than sugar if you like it sweet.
  • Have a glass of grapefruit juice with each meal but make sure it's unsweetened. Try diluting it with sugar-free lemonade if it's too sharp for your tastebuds. Allow 45 calories for a 150ml glass.
  • Make a Florida cocktail and serve as a starter - peel and segment half a grapefruit and one orange and mix with a little unsweetened grapefruit juice.
  • Add grapefruit to salads - it goes well with crab, prawns, chicken, avocado, red onion, celery, raddichio and spinach.
  • Use grapefruit juice as a mixer for alcoholic drinks such as vodka or gin.
  • For special occasions splash out 170 calories on a Seabreeze cocktail - shake 50ml vodka with 75ml each of grapefruit juice and cranberry juice. Serve over ice.

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Fujioka K, Greenway F, Sheard J, Ying Y. The effects of grapefruit on weight and insulin resistance: relationship to the metabolic syndrome. J Med Food. 2006 Spring;9(1):49-54. doi: 10.1089/jmf.2006.9.49. PMID: 16579728.

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