July 26, 2013

Interleukin Genetics, Inc.

135 Beaver Street

Waltham, Massachusetts 02452

Ladies and Gentlemen:

We have acted as legal counsel to Interleukin Genetics, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) of a Registration Statement on Form S-1 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”). The Registration Statement relates to the registration for resale by the selling stockholders named in the Registration Statement (the “Selling Stockholders”) of (i) up to 85,326,230 shares (the “Shares”) of the Company’s common stock, $0.001 par value per share (the “Common Stock”), held by certain selling shareholders (the “Selling Shareholders”) and (ii) up to an additional 35,081,967 shares (the “Warrant Shares”) of Common Stock issuable upon exercise of certain warrants (the “Warrants”) issued to the Selling Shareholders. This opinion is being rendered in connection with the filing of the Registration Statement with the Commission.

In connection with this opinion, we have examined the Company’s Certificate of Incorporation and Amended and Restated Bylaws, each as currently in effect; such other records of the corporate proceedings of the Company and certificates of the Company’s officers as we have deemed relevant; the Warrants; and the Registration Statement and the exhibits thereto.

In our examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified or photostatic copies and the authenticity of the originals of such copies.

Our opinion is limited to the General Corporation Law of the State of Delaware and we express no opinion with respect to the laws of any other jurisdiction. No opinion is expressed herein with respect to the qualification of the Shares or the Warrant Shares under the securities or blue sky laws of any state or any foreign jurisdiction.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. This opinion is based upon currently existing statutes, rules, regulations and judicial decisions, and we disclaim any obligation to advise you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions set forth herein.

Based upon the foregoing, we are of the opinion that (i) the Shares are validly issued, fully paid and non-assessable; and (ii) the Warrant Shares, when issued and delivered in accordance with the terms of the Warrants, will be validly issued, fully paid and non-assessable.

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

Boston | Washington | New York | Stamford | Los Angeles | San Francisco | San Diego | London

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

Page 2

We understand that you wish to file this opinion with the Commission as an exhibit to the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K promulgated under the Securities Act and to reference the firm’s name under the caption “Legal Matters” in the prospectus which forms part of the Registration Statement, and we hereby consent thereto. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.