This is a guest post from Robert Brokamp of The Motley Fool. Robert is a Certified Financial Planner and the adviser for The Motley Fool’s Rule Your Retirement service. He contributes one new article to Get Rich Slowly every two weeks.

Summer’s here, so I’ve been working on my bikini body. But I’m not getting very far. I’ve lost about three pounds over the past three weeks. If you saw me, you may not think that I’m overweight, but that’s only because you haven’t seen me naked (yet). The truth is, as the temperatures became warmer, I pulled my shorts out of storage, and about half of them didn’t fit.

So I’ve been cutting back on the bad carbs and processed foods, and every night my wife and I try to do the DVD exercise program P90X (though it’s often more like P45OUCH). We also get in a couple of runs each week, and I occasionally ride my bike to work. This past weekend, several fellow Fools and I traversed the via ferrata in the mountains of West Virginia, which was exhilarating and exhausting. (Here’s a video made by my colleague, “Shaky Buck”; I’m the guy in the light-blue shirt.)

But after three weeks of a better diet and much more exercise, I still have lost just three pounds, and have yet to re-add a pair of shorts back into the rotation. I figure I have to lose at least another 10 more, preferably another 20.

You may be wondering why I’m telling you, the money-minded GRS audience, about my jiggly parts. Well, I think money management and blubber management have a lot in common. They both rely on smart consumption and good habits that, frankly, aren’t a lot of fun. The effects — both good and bad — aren’t noticed immediately, which makes the bad habits seem not so bad, and the good habits not so instantly rewarding.

I’m no expert, but I bet eating and spending affect the same areas of the brain. (Neuroscientists call it the “You’re all mine and no one else can have you” area…I think.) And I think both can induce temporary insanity. It’s almost like a haze, when that primitive, reptilian part of your brain takes over, telling your more evolved, rational brain to just shut up and enjoy what’s comin’. Soon afterward, your frontal lobe awakens from its stupor, and you say to yourself, “Why the heck did I eat/buy that? What was I thinking?”

There’s also the link between eating too much and spending too much on food. However, that link isn’t always so strong. Eating better can actually cost more. If you’d like, we can discuss it over lunch at Whole Foods. You’ll see what I mean.

Fasting for thin and profit
The question I put to you today, gentle reader, is whether it might make sense occasionally to engage in some extreme fiscal or physical fitness in order to see bigger results sooner, which could serve as encouragement to keep going.

I tried this once before with my diet, cutting out everything except vegetables and lean proteins. That included no more caffeine or any kind of sugar. After a few days, I didn’t feel so great — kinda like I had the flu. I mentioned this to a nutritionist, and she said, “Your body isn’t made to tolerate such extreme changes. It is revolting.” (To which I replied, “Many women find my body revolting.”) So I added back coffee and cereal to my diet, which eventually led to bread and pasta, which eventually led to chocolate milk and ice cream, and, ultimately, chocolate-covered lard. The slippery slope is greased with Hershey syrup.

But now I wonder — after giving in a bit this weekend and consuming some not-so-healthy foods, partially out of discouragement — if a radical change wouldn’t be the better strategy, at least for a while. Wouldn’t I see more results by severely limiting the calories and increasing the exercise, which would inspire me to keep going and stick with it?

The financial equivalent would be a spending diet; over a month (or two or — gasp! — three), only spend money on the necessities. No new clothes, no dining out, maybe even suspend the cable service. All books, movies, and periodicals come from the library, or not at all. Perhaps even institute a rule that if you must buy something, you must also sell something of roughly equivalent value on Craigslist or eBay.

Just as you use a scale to keep tabs on your weight, you’d have to monitor the benefits of your spending diet. If you’re in debt, the freed-up cash flow would go to paying it down. Otherwise, it could go into a savings account or retirement account (though if it’s invested in something other than cash, you’ll have to separate the effects of your additional saving from the effects of gyrating markets). The determination and sense of accomplishment could compound along with the savings, and you might just learn that you can get along just fine with some of those expenses you thought were important.

Maybe you’ll save so much money that you can eat whatever junk you want, knowing that your billions can eventually be used to pay MIT scientists to create bionic replacement body parts for you. Sorta like these guys.

J.D.’s note: I dearly, dearly want to embed the photo Robert linked to, but I can’t. It’s an image of Warren Buffett and Bill Gates eating cheeseburgers and milkshakes at the Hollywood Diner in Carter Lake, Iowa. But the photo is from Fortune magazine, and I can’t legally use it here in this context.

OK, maybe a financial fast won’t make you as wealthy as Warren Buffett or Bill Gates (though Buffett’s license plate used to read “THRIFTY”). And, as far as I know, their body parts are still organic. But I do think it’s funny that two of the richest people in the world are eating at a diner. On one hand, you’d think they have the money and the smarts to eat healthier. On the other hand, just looking at the picture makes me want to run salivating to Steak ‘n Shake.

As for severely restricting eating or spending, obviously, it can go too far (as demonstrated, in my opinion, by this person — make sure you check out the last day of her third consecutive 40-day fast). That’s one of the risks. Another: You can’t stick with the extreme changes, and you feel even more like a failure.

Clearly, I’m not quite sure how I feel about all this. But I’m sure that you, being the smart GRS reader that you are, will add your thoughts in the comments below. I certainly hope you do. In the meantime, I’ll be right here, shopping online for a bikini that is more flattering for my figure.

J.D.’s note: Oh my word. I have so much to say on this subject, and I don’t know where to begin. As you all know, I’ve dubbed 2010 the Year of Fitness. My sole goal is to lose 50 pounds, and so far I’m on target. There are absolutely parallels between fitness and finance, but there are many differences, too. I’d write more about this now, but I’ve got to go ride my bike to the gym…

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