Oauth签名，REST API

I am attempting to access the fat secret API.

https://platform.fatsecret.com/api/

I am attempting to create an Oauth signature using the secret key given by fat secret. When I try access the URL to grab the data I get an error saying my Oauth signature is invalid.

I create the signiture using base64_encode and then hash hmac using sha1.

Here is my code with the secret key blanked out, am I creating the signature in an incorrect way? Or can anyone see where I am going wrong.

Thank you

<?php
$requestTokenUrl = "http://platform.fatsecret.com/rest/server.api";
$oauth_consumer_key = "925f5e1a8b674a70b52eabf15f3265e7"; 
$nonce = md5(mt_rand());
$outh_signature = '';
$oauthSignatureMethod = "HMAC-SHA1"; 
$oauthTimestamp = time();
$oauthVersion = "1.0";
$secret_key = "My Secret Key";

$sigKey= $consumer_key . "&";

$sigBase = "method=food.get" . rawurlencode($requestTokenUrl) . "&"
    . rawurlencode("oauth_consumer_key=" . rawurlencode($oauth_consumer_key)
    . "&oauth_nonce=" . rawurlencode($nonce)
    . "&oauth_signature_method=" . rawurlencode($oauthSignatureMethod)
    . "&oauth_timestamp=" . $oauthTimestamp
    . "&oauth_version=" . $oauthVersion);

$oauthSig = base64_encode(hash_hmac('sha1', $secret_key, true));

$requestUrl = $requestTokenUrl . "?"
    . "food_id=33691"
    . "&method=food.get"
    . "&oauth_consumer_key=" . rawurlencode($oauth_consumer_key)
    . "&oauth_nonce=" . rawurlencode($nonce)
    . "&oauth_signature=" . rawurlencode($oauthSig)
    . "&oauth_signature_method=" . rawurlencode($oauthSignatureMethod)
    . "&oauth_timestamp=" . rawurlencode($oauthTimestamp)
    . "&oauth_version=" . rawurlencode($oauthVersion);

var_dump($requestUrl);