Three Servings of Grapefruit /Day Have No Effect on Weight Loss, But Increase Triglycerides and Make a Potentially Deadly Cocktail With A Whole Host of Prescription Meds!

Image 1: Grapefruit does not help with weight loss and, as it turns out, is not even healthy. On the contrary, in conjunction with your favorite statin it is even potentially deadly.

Do you remember the "grapefruit diet" (WebMD)? No? Well, then you are probably male and have always been satisfied with your weight. Otherwise, you would probably have heard how a "magical ingredient" in the subtropical citrus fruit is going kill all those unaesthetic adypocytes, which have made themselves at home on your hips and buttocks, in no time... What do you say? Bullsh*t? Well, I guess you have been reading to much of my stuff already, after all this purported short-cut to six-pack abs is also known as the Hollywood Diet and that alone will have people fall for it by the dozen... I mean, if Brooke Shields and Kylie Minogue got in shape with it, it must be working, right?

The myth and the truth about grapefruits

I know that you would never be so stupid to start eating nothing but grapefruit (you would not, right?), but despite the fact that the Grapefruit Diet has rightly gotten a bad rep within the (self-)educated members and followers of the wealth of good and not-so-good blogs and websites dealing with nutrition and weight loss, many people still believe that there must be something about this fruit that will help you lose weight. And in view of the fact that I myself know a couple of these (interestingly all female) unfortunate critters, I believe that it is still worth to take a closer look at the results of a recently published study on the effects of 1.5 fresh Rio-Red grapefruit per day on the outcomes of a 6-week dietary intervention (Dow. 2012). The study involved 74 male and female subjects (age: 41y; BMI: 32kg/m²; Bodyfat: 35.7%) who, despite having problems with their weight, had been weight-stable in the past 6 months (or more). After an initial 3-week "wash out period" in the course of which the subjects had to follow a diet that was restricted in bioactive-rich fruits and vegetables (the intention, here, was to get all to a baseline level as far as the purported "magic fat loss ingredient" in citrus fruits is concerned), the subjects were randomized to one of two groups:

1. intervention group (n=42) continued eating the "wash-out diet" and supplemented with their 3x0.5 Rio-Red grapefruit per day 15 minutes prior to their regular three meals
    
2. control group (n=32) continued eating the "wash-out diet"

The dietary intake of the subjects, was evaluated with your usual (unreliable, but in want of alternatives obligatory) repeated 24-hour diet recalls (3x during the washout phase and 3x during the intervention phase). Things like the total caloric intake (1800-1900kcal) or the macronutrient composition did not really differ between diets - in other words: The scientists did a pretty good job to isolate the grapefruit intake and the (obviously) correlating vitamin C intake (cf. figure 1) as the single confounding factors in their study.

Figure 1: Total caloric intake, the number of vegetable servings, the overall macronutrient ratio etc. all were identical between the two groups, except the fruit and (consequently) the vitamin C intake (data based on Dow. 2012)

With a subject pool of 74 men and women and virtually identical diets, we should thusly well be able to see an effect on body weight, body fat, lipid or glucose metablism, if there was one, but as the data in figure 2 indicates, "the magic just did not happen":

Figure 2: Relative changes in anthropometric data in the course of the 6-week study period; no statistically significant inter-group differences, not even statistical significant pre-post changes (data based on Dow. 2012)

Aside from the fact that grapefruit does not make you lose fat, the graph in figure 2 carries another important message, which is: Never use a body impedance device to track your progress. And this goes for all those stupid things, and not only the Omron Body Fat Analyzer HBF-306 which was used in the study. Why? Well, take a look at the body fat and the waist circumference data: How can your gut become smaller, when your body fat percentage increases? The answer is easy, because the grapefruit eaters lost water, they lost ~1% more of their waist circumference. This did yet change the impedance of their bodies so that the stupid for the Omron was tricked to believe that the body fat percentage of the study participants had increased (if you are at a loss how you can track your progress, make sure you read the Intermittent Thoughts on "Stocktaking, Goalsetting, -Tracking & -Resetting").

"But, Dr. Andro, weight loss is not everything" - Correct! And another reason not to eat huge amounts of grapefruits

Another argument of the "grapefruit fanatics" is that, although the weight loss effects of the fruit may be negligible, it still is a healthy superfood that will improve your overall and metabolic health... now, if we take a look at what (unfortunately) is still considered the "gold-standard" as far as the assessment of CVD risk is concerned, i.e. the allmighty lipid profile (imagine a fanfare, here), I guess that only those of you who still believe in the black-and-white version of the lipid hypothesis (HDL = good guy; LDL = bad guy; nothing else counts) will wholeheartedly agree with Dow et al. conclusion that ...

grapefruit consumption does elicit beneficial effects compared with baseline values that are
associated with CVD risk reduction.

If you take a look at the actual data in figure 3 you can hardly argue that the 1.5 grapefruits à day gave the "bad guy" (LDL) a slightly more thorough beating than the "wash out diet" with its quasi non-existent polyphenol content, but...

Figure 3: Changes in lipid profile (unadjusted and adjusted with ANCOVA for BMI, age, sex, and washout-phase p-values) for the control and grapefruit group (left) and the questionable conclusion the scientists draw based on the observed reduction in LDL and statistically likewise non-significantly greater reductions in blood pressure in the grapefruit group (right) (based on Dow. 2012)

...with a p-value (indicating the probability that this is mere coincidence; p < 0.05 is considered "statistically significant) of p = 0.871 for the inter-group difference this difference did not only fail to reach statistical significance, it must also be seen in the context of an increase in triglyceride levels (instead of a decrease in the control group), of which a 2009 study by Kannel et al. states that

[...n]onfasting triglycerides maintained an independent graded relationship with CVD in fully adjusted analyses, with elevated 4 h postprandial triglyceride imposing a 4.5-fold increment relative to lower levels [...and that] triglyceride-associated CVD risk occurs even in patients with low low-density lipoprotein cholesterol (Kannel. 2009)

Just to make sure nobody is missing the point here, neither the inter-group differences in LDL reduction nor the different outcomes as far as the trigs are concerned, reached statistical significance, but against the background of the results of the meta-analysis of Kannel and Vasan from 2009 and recent findings on the contribution of elevated triglyceride levels to the etiology of cardiovascular and metabolic diseases, I personally feel that beyond not helping with weight / fat loss, eating grapefruit could potentially even contribute to, or aggravate existing metabolic disturbances.

If you are on any medication grapefruit is a no-go, anyway!

Image 2: If you are healthy eating grapefruits from time to time won't hurt. If you are taking medication, however, it can potentially be fatal - although I's say that the meds, not the fruit are to blame for this

Yet even if you don't care about the pro-diabetic effects of triglycerides and discard the non-existent effect of grapefruits on weight loss / body composition, there is another, probably more important, because potentially fatal side-effects of eating grapefruit (or drinking its juice / taking respective supplements), which relates to the inhibitory effects it exerts on a hitherto not fully elucidated number of liver enzymes in the cytochrome cascade (CYP), which is heavily involved in drug and hormone metabolism. So, even if you don't take a statin, of which Dreier et al. have shown that it can induce profound rhabdamyolysis (=total break down of muscle protein, which can lead to kidney failure and death), when the grapfruit flavenoids and polyphenols block its metabolism in the liver (Dreier. 2004), or any other of the countless drugs the effects of which are profoundly modulated by the ingestion of grapfruit or grapefruit juice (Hanley. 2011), you better stick to no more than a single grape-fruit once in a while... I mean, it has no beneficial health / weight loss effect, anyway.